Fix Stripe receipt_email + online payment surcharge and hardening

Remove receipt_email from PaymentIntent creation so customers can use
any email at Stripe checkout without a stored-email mismatch blocking
payment. Remove now-dead CustomerEmail from PaymentPageViewModel.

Fix surcharge payment input: amount field now represents the total the
customer pays (including fee); JS back-calculates base before sending
to server. Add InvariantCulture to numeric Razor→JS literals to prevent
comma-decimal cultures from truncating surcharge values.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Application/Interfaces/IStripeConnectService.cs

@@ -20,7 +20,6 @@ public interface IStripeConnectService
         decimal invoiceTotal,
         decimal surchargeAmount,
         string currency,
-        string customerEmail,
         string invoiceNumber,
         int invoiceId);
 
@@ -33,7 +32,6 @@ public interface IStripeConnectService
         decimal depositAmount,
         decimal surchargeAmount,
         string currency,
-        string customerEmail,
         string quoteNumber,
         int quoteId);
 }

src/PowderCoating.Infrastructure/Services/StripeConnectService.cs

@@ -162,7 +162,6 @@ public class StripeConnectService : IStripeConnectService
         decimal invoiceTotal,
         decimal surchargeAmount,
         string currency,
-        string customerEmail,
         string invoiceNumber,
         int invoiceId)
     {
@@ -175,7 +174,6 @@ public class StripeConnectService : IStripeConnectService
             {
                 Amount = amountInCents,
                 Currency = currency.ToLower(),
-                ReceiptEmail = customerEmail,
                 Description = $"Invoice {invoiceNumber}",
                 Metadata = new Dictionary<string, string>
                 {
@@ -215,7 +213,6 @@ public class StripeConnectService : IStripeConnectService
         decimal depositAmount,
         decimal surchargeAmount,
         string currency,
-        string customerEmail,
         string quoteNumber,
         int quoteId)
     {
@@ -228,7 +225,6 @@ public class StripeConnectService : IStripeConnectService
             {
                 Amount = amountInCents,
                 Currency = currency.ToLower(),
-                ReceiptEmail = customerEmail,
                 Description = $"Deposit for quote {quoteNumber}",
                 Metadata = new Dictionary<string, string>
                 {

src/PowderCoating.Web/Controllers/PaymentController.cs

@@ -75,7 +75,6 @@ public class PaymentController : Controller
             CustomerName     = customer != null
                 ? $"{customer.ContactFirstName} {customer.ContactLastName}".Trim()
                 : "Valued Customer",
-            CustomerEmail    = customer?.Email ?? string.Empty,
             CompanyName      = company!.CompanyName,
             BalanceDue       = invoice.BalanceDue,
             InvoiceTotal     = invoice.Total,
@@ -127,8 +126,6 @@ public class PaymentController : Controller
             return BadRequest(new { error = "Invalid payment amount." });
 
         var surcharge = CalculateSurcharge(request.Amount, company!);
-        var customer = await _context.Customers.AsNoTracking()
-            .FirstOrDefaultAsync(c => c.Id == invoice.CustomerId);
 
         var (success, clientSecret, paymentIntentId, stripeError) =
             await _stripeConnect.CreatePaymentIntentAsync(
@@ -136,7 +133,6 @@ public class PaymentController : Controller
                 invoiceTotal: request.Amount,
                 surchargeAmount: surcharge,
                 currency: "usd",
-                customerEmail: customer?.Email ?? string.Empty,
                 invoiceNumber: invoice.InvoiceNumber,
                 invoiceId: invoice.Id);
 
@@ -261,7 +257,6 @@ public class PaymentController : Controller
             CustomerName         = customer != null
                 ? $"{customer.ContactFirstName} {customer.ContactLastName}".Trim()
                 : quote.ProspectContactName ?? "Valued Customer",
-            CustomerEmail        = customer?.Email ?? quote.ProspectEmail ?? string.Empty,
             CompanyName          = company!.CompanyName,
             DepositAmount        = depositAmount,
             QuoteTotal           = quote.Total,
@@ -296,7 +291,6 @@ public class PaymentController : Controller
 
         var depositAmount = Math.Round(quote!.Total * (quote.DepositPercent / 100m), 2);
         var surcharge = CalculateSurcharge(depositAmount, company!);
-        var customerEmail = quote.Customer?.Email ?? quote.ProspectEmail ?? string.Empty;
 
         var (success, clientSecret, paymentIntentId, stripeError) =
             await _stripeConnect.CreateDepositPaymentIntentAsync(
@@ -304,7 +298,6 @@ public class PaymentController : Controller
                 depositAmount: depositAmount,
                 surchargeAmount: surcharge,
                 currency: "usd",
-                customerEmail: customerEmail,
                 quoteNumber: quote.QuoteNumber,
                 quoteId: quote.Id);
 
@@ -942,7 +935,6 @@ public class PaymentPageViewModel
     public int InvoiceId { get; set; }
     public string Token { get; set; } = string.Empty;
     public string CustomerName { get; set; } = string.Empty;
-    public string CustomerEmail { get; set; } = string.Empty;
     public string CompanyName { get; set; } = string.Empty;
     public decimal BalanceDue { get; set; }
     public decimal InvoiceTotal { get; set; }
@@ -963,7 +955,6 @@ public class DepositPaymentPageViewModel
     public int    QuoteId              { get; set; }
     public string Token                { get; set; } = string.Empty;
     public string CustomerName         { get; set; } = string.Empty;
-    public string CustomerEmail        { get; set; } = string.Empty;
     public string CompanyName          { get; set; } = string.Empty;
     public decimal DepositAmount       { get; set; }
     public decimal QuoteTotal          { get; set; }

src/PowderCoating.Web/Views/Payment/Index.cshtml

@@ -75,11 +75,11 @@
                 <div class="input-group mb-1">
                     <span class="input-group-text">$</span>
                     <input type="number" id="paymentAmount" class="form-control"
-                           value="@Model.BalanceDue.ToString("F2")"
+                           value="@Model.TotalWithSurcharge.ToString("F2")"
-                           min="0.01" max="@Model.BalanceDue.ToString("F2")" step="0.01"
+                           min="0.01" max="@Model.TotalWithSurcharge.ToString("F2")" step="0.01"
                            oninput="updateSurcharge()" />
                 </div>
-                <div class="form-text">Max: @Model.BalanceDue.ToString("C")</div>
+                <div class="form-text">Max: @Model.TotalWithSurcharge.ToString("C")</div>
             </div>
         </div>
 
@@ -116,18 +116,17 @@
     const STRIPE_PK  = '@Model.StripePublishableKey';
     const ACCOUNT_ID = '@Model.StripeAccountId';
     const TOKEN      = '@Model.Token';
-    const MAX_AMOUNT = @Model.BalanceDue.ToString("F2");
+    const MAX_TOTAL  = @Model.TotalWithSurcharge.ToString("F2", System.Globalization.CultureInfo.InvariantCulture);
     const SURCHARGE_TYPE  = '@Model.SurchargeType';
-    const SURCHARGE_VALUE = @Model.SurchargeValue.ToString("F4");
+    const SURCHARGE_VALUE = @Model.SurchargeValue.ToString("F4", System.Globalization.CultureInfo.InvariantCulture);
     const SUCCESS_URL = `/pay/${TOKEN}/success`;
 
     const stripe = Stripe(STRIPE_PK, { stripeAccount: ACCOUNT_ID });
     let elements, paymentElement;
 
     async function initStripe() {
-        const amount = parseFloat(document.getElementById('paymentAmount').value) || MAX_AMOUNT;
+        // Input value is the total the customer pays (including fee)
-        const surcharge = calcSurcharge(amount);
+        const total = parseFloat(document.getElementById('paymentAmount').value) || MAX_TOTAL;
-        const total = Math.round((amount + surcharge) * 100) / 100;
 
         elements = stripe.elements({
             mode: 'payment',
@@ -141,12 +140,15 @@
         paymentElement.mount('#payment-element');
     }
 
-    function calcSurcharge(amount) {
+    // Back-calculates the base invoice amount from a total that includes the fee.
+    // Server receives the base and adds surcharge on top — both paths arrive at the same
+    // PaymentIntent amount so Stripe.js never sees an amount mismatch.
+    function calcBaseFromTotal(total) {
         if (SURCHARGE_TYPE === 'Percent')
-            return Math.round(amount * (SURCHARGE_VALUE / 100) * 100) / 100;
+            return Math.round(total / (1 + SURCHARGE_VALUE / 100) * 100) / 100;
         if (SURCHARGE_TYPE === 'Flat')
-            return SURCHARGE_VALUE;
+            return Math.max(0, Math.round((total - SURCHARGE_VALUE) * 100) / 100);
-        return 0;
+        return total;
     }
 
     function formatCurrency(val) {
@@ -154,9 +156,9 @@
     }
 
     function updateSurcharge() {
-        const amount = Math.min(parseFloat(document.getElementById('paymentAmount').value) || 0, MAX_AMOUNT);
+        const total = Math.min(parseFloat(document.getElementById('paymentAmount').value) || 0, MAX_TOTAL);
-        const surcharge = calcSurcharge(amount);
+        const base = calcBaseFromTotal(total);
-        const total = amount + surcharge;
+        const surcharge = Math.round((total - base) * 100) / 100;
 
         const surchargeEl = document.getElementById('surchargeDisplay');
         const totalEl = document.getElementById('totalWithSurchargeDisplay');
@@ -164,7 +166,10 @@
 
         if (surchargeEl) surchargeEl.textContent = formatCurrency(surcharge);
         if (totalEl) totalEl.textContent = formatCurrency(total);
-        if (btnAmtEl) btnAmtEl.textContent = surcharge > 0 ? formatCurrency(total) : formatCurrency(amount);
+        if (btnAmtEl) btnAmtEl.textContent = formatCurrency(total);
+
+        // Keep Elements in sync so confirmPayment amount matches the PaymentIntent
+        if (elements) elements.update({ amount: Math.round(total * 100) });
     }
 
     async function submitPayment() {
@@ -172,13 +177,21 @@
         const msgEl = document.getElementById('payment-message');
         const amountInput = document.getElementById('paymentAmount');
 
-        const amount = parseFloat(amountInput.value);
+        const total = parseFloat(amountInput.value);
-        if (!amount || amount <= 0 || amount > MAX_AMOUNT) {
+        if (!total || total <= 0 || total > MAX_TOTAL) {
             msgEl.textContent = 'Please enter a valid payment amount.';
             msgEl.style.display = '';
             return;
         }
 
+        // Back-calculate base; server adds surcharge on top as usual
+        const base = calcBaseFromTotal(total);
+        if (base <= 0) {
+            msgEl.textContent = 'Payment amount must exceed the convenience fee.';
+            msgEl.style.display = '';
+            return;
+        }
+
         btn.disabled = true;
         document.getElementById('submitText').style.display = 'none';
         document.getElementById('submitSpinner').style.display = '';
@@ -195,13 +208,13 @@
             return;
         }
 
-        // Create PaymentIntent on server
+        // Create PaymentIntent on server — send base amount (server adds surcharge)
         let clientSecret;
         try {
             const resp = await fetch(`/pay/${TOKEN}/intent`, {
                 method: 'POST',
                 headers: { 'Content-Type': 'application/json' },
-                body: JSON.stringify({ amount })
+                body: JSON.stringify({ amount: base })
             });
             const data = await resp.json();
             if (!resp.ok) {