diff --git a/.env.example b/.env.example
index 793313e..ef35eef 100644
--- a/.env.example
+++ b/.env.example
@@ -83,6 +83,14 @@ SEED_ADMIN_PASSWORD=change-me-strong-admin-password
 ZARINPAL_MERCHANT_ID=
 ZARINPAL_SANDBOX=false
 
+# ── Payment: FlatRender Pay (ZarinPal broker) ─────────────────────────────────
+# Broker keys from the FlatRender dashboard. Webhook is registered at the broker as
+# https://api.meezi.ir/api/payment/webhook. Keep the live secret OUT of git.
+FLATPAY_API_KEY=
+FLATPAY_SECRET=
+FLATPAY_BASE_URL=https://pay.flatrender.ir
+FLATPAY_RETURN_URL=https://meezi.ir/payment/return
+
 # ── SMS: Kavenegar ────────────────────────────────────────────────────────────
 # Empty = OTP is logged to API console (fine for dev, not for production)
 KAVENEGAR_API_KEY=4C30786935496261332B41685870444E47657A5367453369374F6E2F43334672576B526F5A4B4B795665493D
diff --git a/docker-compose.yml b/docker-compose.yml
index 7741582..6984262 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -94,6 +94,10 @@ services:
       Snappfood__WebhookSecret: "${SNAPPFOOD_WEBHOOK_SECRET:-meezi-dev-snappfood-secret}"
       ZarinPal__MerchantId: "${ZARINPAL_MERCHANT_ID:-}"
       ZarinPal__Sandbox: "${ZARINPAL_SANDBOX:-true}"
+      FlatPay__ApiKey: "${FLATPAY_API_KEY:-}"
+      FlatPay__Secret: "${FLATPAY_SECRET:-}"
+      FlatPay__BaseUrl: "${FLATPAY_BASE_URL:-https://pay.flatrender.ir}"
+      FlatPay__ReturnUrl: "${FLATPAY_RETURN_URL:-https://meezi.ir/payment/return}"
       Seed__SystemAdminPhone: "${SEED_ADMIN_PHONE:-}"
       Seed__SystemAdminUsername: "${SEED_ADMIN_USERNAME:-admin}"
       Seed__SystemAdminPassword: "${SEED_ADMIN_PASSWORD:-}"
diff --git a/src/Meezi.API/Controllers/PaymentController.cs b/src/Meezi.API/Controllers/PaymentController.cs
new file mode 100644
index 0000000..9a9df8c
--- /dev/null
+++ b/src/Meezi.API/Controllers/PaymentController.cs
@@ -0,0 +1,129 @@
+using System.Text.Json;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using Meezi.API.Models.Payments;
+using Meezi.API.Services;
+using Meezi.API.Services.Payments;
+using Meezi.Core.Authorization;
+using Meezi.Core.Enums;
+using Meezi.Core.Interfaces;
+using Meezi.Shared;
+
+namespace Meezi.API.Controllers;
+
+/// <summary>FlatRender Pay (ZarinPal broker) checkout + webhook.</summary>
+[ApiController]
+public class PaymentController : CafeApiControllerBase
+{
+    private readonly IBillingService _billing;
+    private readonly IFlatPayService _flatPay;
+    private readonly ILogger<PaymentController> _logger;
+
+    public PaymentController(IBillingService billing, IFlatPayService flatPay, ILogger<PaymentController> logger)
+    {
+        _billing = billing;
+        _flatPay = flatPay;
+        _logger = logger;
+    }
+
+    /// <summary>Start a FlatPay checkout for a plan bundle; returns the URL to redirect the buyer to.</summary>
+    [Authorize]
+    [HttpPost("api/payment/request")]
+    public async Task<IActionResult> CreatePayment(
+        [FromBody] PaymentRequestDto request,
+        ITenantContext tenant,
+        CancellationToken ct)
+    {
+        if (EnsurePermission(tenant, Permission.ManageBilling) is { } permDenied) return permDenied;
+        if (string.IsNullOrEmpty(tenant.CafeId)) return Unauthorized();
+
+        if (request?.ProductId is null || !TryParseProduct(request.ProductId, out var tier, out var months))
+            return BadRequest(new ApiResponse<object>(false, null,
+                new ApiError("INVALID_PRODUCT", "productId must be a \"Tier:Months\" bundle, e.g. \"Pro:12\".")));
+
+        var (paymentId, amountToman, code, message) =
+            await _billing.CreateFlatPayOrderAsync(tenant.CafeId, tier, months, ct);
+        if (paymentId is null)
+            return BadRequest(new ApiResponse<object>(false, null, new ApiError(code ?? "ERROR", message ?? "Failed.")));
+
+        var description = $"میزی — اشتراک {tier} ({months} ماه)";
+        var url = await _flatPay.RequestAsync(
+            tenant.CafeId, request.ProductId, (long)amountToman, description, paymentId, ct);
+
+        if (string.IsNullOrEmpty(url))
+            return BadRequest(new ApiResponse<object>(false, null,
+                new ApiError("PAYMENT_FAILED", "Could not start the payment.")));
+
+        return Ok(new ApiResponse<PaymentRequestResponse>(true, new PaymentRequestResponse(url, paymentId)));
+    }
+
+    /// <summary>Broker → us. Security is the HMAC signature (no user auth). Always 200 after a valid
+    /// signature so the broker doesn't retry a job we've accepted.</summary>
+    [AllowAnonymous]
+    [HttpPost("api/payment/webhook")]
+    public async Task<IActionResult> Webhook(CancellationToken ct)
+    {
+        using var ms = new MemoryStream();
+        await Request.Body.CopyToAsync(ms, ct);
+        var raw = ms.ToArray();
+
+        var signature = Request.Headers["X-FlatPay-Signature"].ToString();
+        if (!_flatPay.VerifyWebhook(raw, signature))
+            return Unauthorized();
+
+        try
+        {
+            using var doc = JsonDocument.Parse(raw);
+            var root = doc.RootElement;
+
+            var status = GetString(root, "status");
+            var brokerId = GetString(root, "id") ?? GetString(root, "payment_id");
+
+            if (string.Equals(status, "Paid", StringComparison.OrdinalIgnoreCase)
+                && !string.IsNullOrEmpty(brokerId)
+                && _flatPay.TryMarkProcessed(brokerId))
+            {
+                var meta = root.TryGetProperty("metadata", out var m) && m.ValueKind == JsonValueKind.Object
+                    ? m
+                    : default;
+                var paymentId = GetString(meta, "payment_id");
+
+                if (!string.IsNullOrEmpty(paymentId))
+                    await _billing.CompleteFlatPayAsync(paymentId, brokerId, ct);
+                else
+                    _logger.LogWarning("FlatPay webhook Paid but missing metadata.payment_id (broker id {Id})", brokerId);
+            }
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "FlatPay webhook processing error");
+        }
+
+        return Ok();
+    }
+
+    /// <summary>Parse a "Tier:Months" product id, e.g. "Pro:12" → (PlanTier.Pro, 12).</summary>
+    private static bool TryParseProduct(string productId, out PlanTier tier, out int months)
+    {
+        tier = default;
+        months = 0;
+        var parts = productId.Split(':', 2, StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries);
+        if (parts.Length != 2) return false;
+        return Enum.TryParse(parts[0], ignoreCase: true, out tier)
+            && tier != PlanTier.Free
+            && int.TryParse(parts[1], out months)
+            && months > 0;
+    }
+
+    private static string? GetString(JsonElement el, string name)
+    {
+        if (el.ValueKind != JsonValueKind.Object || !el.TryGetProperty(name, out var v))
+            return null;
+        return v.ValueKind switch
+        {
+            JsonValueKind.String => v.GetString(),
+            JsonValueKind.Number => v.ToString(),
+            _ => null,
+        };
+    }
+}
diff --git a/src/Meezi.API/Extensions/ServiceCollectionExtensions.cs b/src/Meezi.API/Extensions/ServiceCollectionExtensions.cs
index 0f057a9..3bad869 100644
--- a/src/Meezi.API/Extensions/ServiceCollectionExtensions.cs
+++ b/src/Meezi.API/Extensions/ServiceCollectionExtensions.cs
@@ -13,6 +13,7 @@ using Meezi.API.Services;
 using Meezi.API.Services.Delivery;
 using Meezi.Infrastructure.Services.Platform;
 using Meezi.API.Services.Printing;
+using Meezi.API.Services.Payments;
 using Meezi.Core.Interfaces;
 using Meezi.Infrastructure;
 using Serilog;
@@ -95,6 +96,13 @@ public static class ServiceCollectionExtensions
         services.AddScoped<ReceiptBuilder>();
         services.AddScoped<IPrinterService, NetworkPrinterService>();
         services.AddSingleton<IPrintAgentRegistry, PrintAgentRegistry>();
+        services.Configure<FlatPayOptions>(configuration.GetSection(FlatPayOptions.SectionName));
+        services.AddHttpClient<IFlatPayService, FlatPayService>((sp, c) =>
+        {
+            var baseUrl = configuration["FlatPay:BaseUrl"];
+            c.BaseAddress = new Uri(string.IsNullOrWhiteSpace(baseUrl) ? "https://pay.flatrender.ir" : baseUrl);
+            c.Timeout = TimeSpan.FromSeconds(30);
+        });
         services.AddHttpClient(nameof(PosDeviceService));
         services.AddScoped<IPosDeviceService, PosDeviceService>();
         services.AddScoped<SubscriptionRenewalReminderJob>();
diff --git a/src/Meezi.API/Models/Payments/PaymentDtos.cs b/src/Meezi.API/Models/Payments/PaymentDtos.cs
new file mode 100644
index 0000000..2c0a883
--- /dev/null
+++ b/src/Meezi.API/Models/Payments/PaymentDtos.cs
@@ -0,0 +1,6 @@
+namespace Meezi.API.Models.Payments;
+
+/// <summary>Body for POST /api/payment/request. ProductId is a "Tier:Months" bundle, e.g. "Pro:12".</summary>
+public record PaymentRequestDto(string ProductId);
+
+public record PaymentRequestResponse(string Url, string PaymentId);
diff --git a/src/Meezi.API/Services/BillingService.cs b/src/Meezi.API/Services/BillingService.cs
index 7ba93c3..1943297 100644
--- a/src/Meezi.API/Services/BillingService.cs
+++ b/src/Meezi.API/Services/BillingService.cs
@@ -40,6 +40,21 @@ public interface IBillingService
         string cafeId,
         string paymentId,
         CancellationToken cancellationToken = default);
+
+    /// <summary>Price a plan+months bundle and create a Pending FlatPay SubscriptionPayment
+    /// (the "order"); the returned id is passed to the broker as client_ref / metadata.payment_id.</summary>
+    Task<(string? PaymentId, decimal AmountToman, string? ErrorCode, string? Message)> CreateFlatPayOrderAsync(
+        string cafeId,
+        PlanTier tier,
+        int months,
+        CancellationToken cancellationToken = default);
+
+    /// <summary>Grant a FlatPay order after the broker reports it Paid: activate the plan using
+    /// the same coverage/queueing logic as the other providers. Idempotent.</summary>
+    Task<bool> CompleteFlatPayAsync(
+        string paymentId,
+        string? refId,
+        CancellationToken cancellationToken = default);
 }
 
 public class BillingService : IBillingService
@@ -217,6 +232,16 @@ public class BillingService : IBillingService
 
         payment.RefId = verify.RefId;
 
+        await ActivatePaymentAsync(payment, cancellationToken);
+
+        return new BillingVerifyResult(true, successUrl);
+    }
+
+    /// <summary>Apply a paid SubscriptionPayment: book it after the current coverage (queued) or
+    /// activate it now, update the cafe plan, persist, and send the confirmation SMS. Shared by all
+    /// providers (gateway callbacks and the FlatPay webhook).</summary>
+    private async Task ActivatePaymentAsync(SubscriptionPayment payment, CancellationToken cancellationToken)
+    {
         var cafe = payment.Cafe;
         var now = DateTime.UtcNow;
 
@@ -244,8 +269,75 @@ public class BillingService : IBillingService
         await _db.SaveChangesAsync(cancellationToken);
 
         await TrySendConfirmationSmsAsync(cafe, payment, queued, cancellationToken);
+    }
 
-        return new BillingVerifyResult(true, successUrl);
+    public async Task<(string? PaymentId, decimal AmountToman, string? ErrorCode, string? Message)> CreateFlatPayOrderAsync(
+        string cafeId,
+        PlanTier tier,
+        int months,
+        CancellationToken cancellationToken = default)
+    {
+        if (months is < 1 or > 36)
+            return (null, 0m, "INVALID_MONTHS", "Months must be between 1 and 36.");
+
+        var cafe = await _db.Cafes.FirstOrDefaultAsync(c => c.Id == cafeId, cancellationToken);
+        if (cafe is null)
+            return (null, 0m, "NOT_FOUND", "Cafe not found.");
+
+        if (!await _platformCatalog.IsBillableOnlineAsync(tier, cancellationToken))
+            return (null, 0m, "NOT_BILLABLE", "This plan requires contacting sales.");
+
+        var monthly = await _platformCatalog.GetMonthlyPriceTomanAsync(tier, cancellationToken);
+        if (monthly <= 0)
+            return (null, 0m, "NOT_BILLABLE", "This plan has no online price.");
+
+        var amountToman = monthly * months;
+        var payment = new SubscriptionPayment
+        {
+            CafeId = cafeId,
+            PlanTier = tier,
+            Months = months,
+            AmountToman = amountToman,
+            AmountRials = PlanPricing.ToRials(amountToman),
+            Provider = PaymentProvider.FlatPay,
+            Status = SubscriptionPaymentStatus.Pending,
+        };
+
+        _db.SubscriptionPayments.Add(payment);
+        await _db.SaveChangesAsync(cancellationToken);
+
+        return (payment.Id, amountToman, null, null);
+    }
+
+    public async Task<bool> CompleteFlatPayAsync(
+        string paymentId,
+        string? refId,
+        CancellationToken cancellationToken = default)
+    {
+        if (string.IsNullOrWhiteSpace(paymentId))
+            return false;
+
+        var payment = await _db.SubscriptionPayments
+            .Include(p => p.Cafe)
+            .FirstOrDefaultAsync(
+                p => p.Id == paymentId && p.Provider == PaymentProvider.FlatPay,
+                cancellationToken);
+
+        if (payment is null)
+        {
+            _logger.LogWarning("FlatPay grant: no pending order {PaymentId}", paymentId);
+            return false;
+        }
+
+        // Already granted (webhook redelivery / double-process) → idempotent no-op.
+        if (payment.Status is SubscriptionPaymentStatus.Completed or SubscriptionPaymentStatus.Scheduled)
+            return true;
+
+        payment.RefId = refId;
+        await ActivatePaymentAsync(payment, cancellationToken);
+        _logger.LogInformation("FlatPay grant applied: payment {PaymentId} → {Tier} x{Months}m",
+            payment.Id, payment.PlanTier, payment.Months);
+        return true;
     }
 
     /// <summary>End of the cafe's current paid coverage: the later of its active plan expiry
diff --git a/src/Meezi.API/Services/Payments/FlatPayService.cs b/src/Meezi.API/Services/Payments/FlatPayService.cs
new file mode 100644
index 0000000..7979890
--- /dev/null
+++ b/src/Meezi.API/Services/Payments/FlatPayService.cs
@@ -0,0 +1,151 @@
+using System.Collections.Concurrent;
+using System.Net.Http.Headers;
+using System.Security.Cryptography;
+using System.Text;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using Microsoft.Extensions.Options;
+
+namespace Meezi.API.Services.Payments;
+
+public sealed class FlatPayOptions
+{
+    public const string SectionName = "FlatPay";
+
+    public string ApiKey { get; set; } = "";
+    public string Secret { get; set; } = "";
+    public string BaseUrl { get; set; } = "https://pay.flatrender.ir";
+    public string ReturnUrl { get; set; } = "https://meezi.ir/payment/return";
+}
+
+/// <summary>
+/// Client for the FlatRender Pay broker (a ZarinPal front). Requests are authenticated
+/// with <c>X-Api-Key</c> + <c>X-Signature</c> = hex(HMAC-SHA256(secret, raw JSON bytes));
+/// webhooks are verified the same way. The signature is computed over the EXACT bytes
+/// that are sent/received, so we serialize once and reuse the buffer.
+/// </summary>
+public interface IFlatPayService
+{
+    /// <summary>Create a payment at the broker and return its hosted payment URL (null on failure).
+    /// <paramref name="clientRef"/> is echoed back and also embedded in metadata.payment_id.</summary>
+    Task<string?> RequestAsync(
+        string userId, string productId, long amountToman, string description, string clientRef,
+        CancellationToken ct = default);
+
+    /// <summary>Fixed-time compare hex(HMAC(secret, rawBytes)) against the webhook signature header.</summary>
+    bool VerifyWebhook(byte[] rawBytes, string? signature);
+
+    /// <summary>Idempotency: true only the first time a given broker payment id is seen.</summary>
+    bool TryMarkProcessed(string id);
+}
+
+public sealed class FlatPayService : IFlatPayService
+{
+    private readonly HttpClient _http;
+    private readonly FlatPayOptions _opts;
+    private readonly ILogger<FlatPayService> _logger;
+
+    // Webhooks can be redelivered; remember the broker ids we've already granted.
+    private readonly ConcurrentDictionary<string, byte> _seen = new();
+
+    public FlatPayService(HttpClient http, IOptions<FlatPayOptions> opts, ILogger<FlatPayService> logger)
+    {
+        _http = http;
+        _opts = opts.Value;
+        _logger = logger;
+    }
+
+    public async Task<string?> RequestAsync(
+        string userId, string productId, long amountToman, string description, string clientRef,
+        CancellationToken ct = default)
+    {
+        var body = new PayRequestBody(
+            amountToman,
+            "IRT",
+            description,
+            clientRef,
+            _opts.ReturnUrl,
+            new PayMetadata(userId, productId, clientRef));
+
+        // Serialize once: these exact bytes are both signed and sent.
+        var bytes = JsonSerializer.SerializeToUtf8Bytes(body);
+
+        using var req = new HttpRequestMessage(HttpMethod.Post, "/v1/pay/request");
+        req.Content = new ByteArrayContent(bytes);
+        req.Content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
+        req.Headers.TryAddWithoutValidation("X-Api-Key", _opts.ApiKey);
+        req.Headers.TryAddWithoutValidation("X-Signature", Sign(bytes));
+
+        try
+        {
+            using var resp = await _http.SendAsync(req, ct);
+            var respBody = await resp.Content.ReadAsStringAsync(ct);
+            if (!resp.IsSuccessStatusCode)
+            {
+                _logger.LogError("FlatPay /v1/pay/request failed {Status}: {Body}", (int)resp.StatusCode, respBody);
+                return null;
+            }
+
+            using var doc = JsonDocument.Parse(respBody);
+            var url = ExtractPaymentUrl(doc.RootElement);
+            if (string.IsNullOrEmpty(url))
+                _logger.LogError("FlatPay request returned no payment_url: {Body}", respBody);
+            return url;
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "FlatPay request error");
+            return null;
+        }
+    }
+
+    public bool VerifyWebhook(byte[] rawBytes, string? signature)
+    {
+        if (string.IsNullOrWhiteSpace(signature)) return false;
+        var expected = Sign(rawBytes);
+        var provided = signature.Trim().ToLowerInvariant();
+
+        // Compare the ascii hex digests in fixed time.
+        var a = Encoding.ASCII.GetBytes(expected);
+        var b = Encoding.ASCII.GetBytes(provided);
+        return a.Length == b.Length && CryptographicOperations.FixedTimeEquals(a, b);
+    }
+
+    public bool TryMarkProcessed(string id) =>
+        !string.IsNullOrEmpty(id) && _seen.TryAdd(id, 0);
+
+    private string Sign(byte[] body)
+    {
+        using var hmac = new HMACSHA256(Encoding.UTF8.GetBytes(_opts.Secret));
+        return Convert.ToHexString(hmac.ComputeHash(body)).ToLowerInvariant();
+    }
+
+    private static string? ExtractPaymentUrl(JsonElement root)
+    {
+        if (TryGetString(root, "payment_url") is { } direct) return direct;
+        // Some broker responses nest the result under "data".
+        if (root.TryGetProperty("data", out var data) && data.ValueKind == JsonValueKind.Object)
+            return TryGetString(data, "payment_url");
+        return null;
+    }
+
+    private static string? TryGetString(JsonElement el, string name) =>
+        el.ValueKind == JsonValueKind.Object
+        && el.TryGetProperty(name, out var v)
+        && v.ValueKind == JsonValueKind.String
+            ? v.GetString()
+            : null;
+
+    private sealed record PayRequestBody(
+        [property: JsonPropertyName("amount")] long Amount,
+        [property: JsonPropertyName("currency")] string Currency,
+        [property: JsonPropertyName("description")] string Description,
+        [property: JsonPropertyName("client_ref")] string ClientRef,
+        [property: JsonPropertyName("return_url")] string ReturnUrl,
+        [property: JsonPropertyName("metadata")] PayMetadata Metadata);
+
+    private sealed record PayMetadata(
+        [property: JsonPropertyName("user_id")] string UserId,
+        [property: JsonPropertyName("product_id")] string ProductId,
+        [property: JsonPropertyName("payment_id")] string PaymentId);
+}
diff --git a/src/Meezi.API/appsettings.json b/src/Meezi.API/appsettings.json
index 5d705b2..2f26e89 100644
--- a/src/Meezi.API/appsettings.json
+++ b/src/Meezi.API/appsettings.json
@@ -44,6 +44,12 @@
     "MerchantId": "",
     "Sandbox": true
   },
+  "FlatPay": {
+    "BaseUrl": "https://pay.flatrender.ir",
+    "ReturnUrl": "https://meezi.ir/payment/return",
+    "ApiKey": "",
+    "Secret": ""
+  },
   "Billing": {
     "DashboardBaseUrl": "http://localhost:3101"
   },
diff --git a/src/Meezi.Core/Enums/PaymentProvider.cs b/src/Meezi.Core/Enums/PaymentProvider.cs
index ca180ad..709095d 100644
--- a/src/Meezi.Core/Enums/PaymentProvider.cs
+++ b/src/Meezi.Core/Enums/PaymentProvider.cs
@@ -4,7 +4,9 @@ public enum PaymentProvider
 {
     ZarinPal = 0,
     Tara = 1,
-    SnappPay = 2
+    SnappPay = 2,
+    // Appended (stored as int) so existing rows keep their meaning — no migration needed.
+    FlatPay = 3
 }
 
 public static class PaymentProviderIds