diff --git a/apps/edr-freight-web/portal/src/pages/billing/InvoiceDetailPage.tsx b/apps/edr-freight-web/portal/src/pages/billing/InvoiceDetailPage.tsx
index 6fbb15d62..7abadf82f 100644
--- a/apps/edr-freight-web/portal/src/pages/billing/InvoiceDetailPage.tsx
+++ b/apps/edr-freight-web/portal/src/pages/billing/InvoiceDetailPage.tsx
@@ -15,13 +15,22 @@ import {
   Text,
   Title,
 } from "@mantine/core";
-import { ArrowLeft, CreditCard, Download, ExternalLink, Receipt } from "lucide-react";
+import {
+  ArrowLeft,
+  CreditCard,
+  Download,
+  ExternalLink,
+  Receipt,
+} from "lucide-react";
 import { useState } from "react";
 import toast from "react-hot-toast";
 
 import { api } from "@/services/api";
 import { invoicesService } from "@/services/invoices.service";
-import { paymentsService, type PaymentMethod } from "@/services/payments.service";
+import {
+  paymentsService,
+  type PaymentMethod,
+} from "@/services/payments.service";
 import { warehouseInvoicesService } from "@/services/warehouse-invoices.service";
 import { PaymentMethodModal } from "@/pages/bookings/BookingDetailPage/components/PaymentMethodModal";
 import { saveBlob } from "@/utils/download";
@@ -38,7 +47,12 @@ import {
 function MetaItem({ label, value }: { label: string; value: string }) {
   return (
     <Box>
-      <Text fz={11} fw={700} c={MUTED} style={{ textTransform: "uppercase", letterSpacing: "0.05em" }}>
+      <Text
+        fz={11}
+        fw={700}
+        c={MUTED}
+        style={{ textTransform: "uppercase", letterSpacing: "0.05em" }}
+      >
         {label}
       </Text>
       <Text fz={14} mt={4} style={{ color: INK }}>
@@ -52,30 +66,25 @@ export default function InvoiceDetailPage() {
   const { id = "" } = useParams();
   const navigate = useNavigate();
 
-  const { data: invoice, isLoading, isError } = useQuery(
-    api.invoices.get.queryOptions({ input: { id } }),
-  );
+  const {
+    data: invoice,
+    isLoading,
+    isError,
+  } = useQuery(api.invoices.get.queryOptions({ input: { id } }));
 
   const [payModalOpen, setPayModalOpen] = useState(false);
 
-  // Extracted for payMutation callbacks — guaranteed defined when they run
-  // (guarded by the early return below).
-  const invSource = invoice?.source;
-  const invSourceId = invoice?.sourceId;
-
+  // Ownership-checked: POST /billing/my-invoices/:id/pay only ever charges
+  // one of the signed-in customer's own invoices (unlike the admin-facing
+  // /payments/initiate, which takes any invoiceId with no ownership check).
   const payMutation = useMutation({
-    mutationFn: async (method: PaymentMethod) => {
-      const bookingId =
-        invSource === "warehouse"
-          ? (await warehouseInvoicesService.get(id)).bookingId ?? invSourceId!
-          : invSourceId!;
-      return api.payments.initiate.call({ bookingId, method });
-    },
+    mutationFn: (method: PaymentMethod) =>
+      api.invoices.pay.call({ id, payload: { method, platform: "web" } }),
     onSuccess: (data, method) => {
       const redirectUrl =
         data?.clientAction?.type === "REDIRECT" && data.clientAction.url
           ? data.clientAction.url
-          : paymentsService.checkoutUrl({ bookingId: invSourceId!, method });
+          : paymentsService.checkoutUrlForInvoice({ invoiceId: id, method });
       window.location.href = redirectUrl;
     },
   });
@@ -180,7 +189,12 @@ export default function InvoiceDetailPage() {
         {/* Header */}
         <Group justify="space-between" align="flex-start" wrap="wrap" gap="md">
           <Group gap={12} align="center" wrap="wrap">
-            <Title order={1} fw={800} fz={26} style={{ letterSpacing: "-0.01em" }}>
+            <Title
+              order={1}
+              fw={800}
+              fz={26}
+              style={{ letterSpacing: "-0.01em" }}
+            >
               {invoice.invoiceNumber}
             </Title>
             <InvoiceStatusBadge status={invoice.status} />
@@ -193,7 +207,9 @@ export default function InvoiceDetailPage() {
                 size="md"
                 leftSection={<ExternalLink size={16} />}
                 onClick={viewSource}
-                styles={{ root: { fontWeight: 600, height: 42, paddingInline: 16 } }}
+                styles={{
+                  root: { fontWeight: 600, height: 42, paddingInline: 16 },
+                }}
               >
                 View source
               </Button>
@@ -204,7 +220,9 @@ export default function InvoiceDetailPage() {
               size="md"
               leftSection={<Download size={16} />}
               onClick={downloadInvoice}
-              styles={{ root: { fontWeight: 600, height: 42, paddingInline: 16 } }}
+              styles={{
+                root: { fontWeight: 600, height: 42, paddingInline: 16 },
+              }}
             >
               Download invoice
             </Button>
@@ -216,7 +234,9 @@ export default function InvoiceDetailPage() {
                 size="md"
                 leftSection={<Receipt size={16} />}
                 onClick={downloadReceipt}
-                styles={{ root: { fontWeight: 600, height: 42, paddingInline: 16 } }}
+                styles={{
+                  root: { fontWeight: 600, height: 42, paddingInline: 16 },
+                }}
               >
                 Receipt
               </Button>
@@ -229,9 +249,12 @@ export default function InvoiceDetailPage() {
                 leftSection={<CreditCard size={16} />}
                 loading={payMutation.isPending}
                 onClick={handlePay}
-                styles={{ root: { fontWeight: 600, height: 42, paddingInline: 18 } }}
+                styles={{
+                  root: { fontWeight: 600, height: 42, paddingInline: 18 },
+                }}
               >
-                Pay {formatCurrency(Number(invoice.totalAmount), invoice.currency)}
+                Pay{" "}
+                {formatCurrency(Number(invoice.totalAmount), invoice.currency)}
               </Button>
             )}
           </Group>
@@ -241,7 +264,10 @@ export default function InvoiceDetailPage() {
         <Paper withBorder radius="lg" p="lg" style={{ borderColor: BORDER }}>
           <SimpleGrid cols={{ base: 1, sm: 2, md: 4 }} spacing="lg">
             <MetaItem label="Billed To" value={billedTo(invoice)} />
-            <MetaItem label="Source" value={`${titleCase(invoice.source)} · ${invoice.type}`} />
+            <MetaItem
+              label="Source"
+              value={`${titleCase(invoice.source)} · ${invoice.type}`}
+            />
             <MetaItem label="Issued" value={fmtDate(invoice.issuedAt)} />
             <MetaItem label="Due" value={fmtDate(invoice.dueAt)} />
           </SimpleGrid>
@@ -249,7 +275,12 @@ export default function InvoiceDetailPage() {
           <Divider my="lg" color={BORDER} />
 
           <Group justify="space-between" align="center">
-            <Text fz={14} fw={700} c={MUTED} style={{ textTransform: "uppercase", letterSpacing: "0.05em" }}>
+            <Text
+              fz={14}
+              fw={700}
+              c={MUTED}
+              style={{ textTransform: "uppercase", letterSpacing: "0.05em" }}
+            >
               Total
             </Text>
             <Text fz={24} fw={800} style={{ color: INK }}>
@@ -349,7 +380,10 @@ export default function InvoiceDetailPage() {
               payMutation.reset();
             }
           }}
-          amountLabel={formatCurrency(Number(invoice.totalAmount), invoice.currency)}
+          amountLabel={formatCurrency(
+            Number(invoice.totalAmount),
+            invoice.currency,
+          )}
           currency={invoice.currency}
           processing={payMutation.isPending}
           error={
diff --git a/apps/edr-freight-web/portal/src/pages/bookings/BookingDetailPage/ReadonlyBookingView.tsx b/apps/edr-freight-web/portal/src/pages/bookings/BookingDetailPage/ReadonlyBookingView.tsx
index 7c2c2631c..9dbb9ed10 100644
--- a/apps/edr-freight-web/portal/src/pages/bookings/BookingDetailPage/ReadonlyBookingView.tsx
+++ b/apps/edr-freight-web/portal/src/pages/bookings/BookingDetailPage/ReadonlyBookingView.tsx
@@ -1,5 +1,5 @@
 import { Box, Group, Text } from "@mantine/core";
-import { useMutation } from "@tanstack/react-query";
+import { useMutation, useQuery } from "@tanstack/react-query";
 import { CreditCard, Download, Eye } from "lucide-react";
 import { useState } from "react";
 import { useNavigate } from "react-router-dom";
@@ -8,7 +8,9 @@ import { isViewable } from "@edr/ui-common";
 import { api } from "@/services/api";
 import { fileViewUrl } from "@/constants/apiConfig";
 import { useFileViewer } from "@/hooks/useFileViewer";
+import { invoicesService } from "@/services/invoices.service";
 import { paymentsService, type PaymentMethod } from "@/services/payments.service";
+import { isPayable } from "@/pages/billing/invoice-ui";
 import type { Freight } from "@edr/types";
 
 import { ApproveDeliveryButton } from "../delivery/ApproveDeliveryButton";
@@ -51,17 +53,41 @@ export function ReadonlyBookingView({ booking }: { booking: Freight.IBooking })
     : "/contracts/new";
   const onRebook = () => navigate(rebookTo);
 
-  // POST /payments/initiate creates the intent and returns the provider's
-  // redirect URL (clientAction.url). Send the browser straight there; fall back
-  // to the public /payments/checkout page if no redirect URL came back.
+  // Billing is invoice-centric — resolve the booking's currently payable
+  // invoice (same query/key BookingPaymentPanel uses, so this shares its
+  // cache) and pay it through the ownership-checked portal route.
+  const { data: bookingInvoices = [] } = useQuery({
+    queryKey: ["booking-invoices", booking.id],
+    queryFn: () => invoicesService.listForSource("booking", booking.id),
+  });
+  const payableInvoiceId = bookingInvoices.find((inv) =>
+    isPayable(inv.status),
+  )?.id;
+
+  // POST /billing/my-invoices/:id/pay creates the intent and returns the
+  // provider's redirect URL (clientAction.url). Send the browser straight
+  // there; fall back to the public /payments/checkout page if no redirect
+  // URL came back.
   const payMutation = useMutation({
-    mutationFn: (method: PaymentMethod) =>
-      api.payments.initiate.call({ bookingId: booking.id, method }),
+    mutationFn: (method: PaymentMethod) => {
+      if (!payableInvoiceId) {
+        throw new Error(
+          "No payable invoice found for this booking yet. Please refresh or contact support.",
+        );
+      }
+      return api.invoices.pay.call({
+        id: payableInvoiceId,
+        payload: { method, platform: "web" },
+      });
+    },
     onSuccess: (data, method) => {
       const redirectUrl =
         data?.clientAction?.type === "REDIRECT" && data.clientAction.url
           ? data.clientAction.url
-          : paymentsService.checkoutUrl({ bookingId: booking.id, method });
+          : paymentsService.checkoutUrlForInvoice({
+              invoiceId: payableInvoiceId!,
+              method,
+            });
       window.location.href = redirectUrl;
     },
   });
diff --git a/apps/edr-freight-web/portal/src/services/payments.service.ts b/apps/edr-freight-web/portal/src/services/payments.service.ts
index 119aea4ed..c62e31108 100644
--- a/apps/edr-freight-web/portal/src/services/payments.service.ts
+++ b/apps/edr-freight-web/portal/src/services/payments.service.ts
@@ -17,7 +17,7 @@ export type PaymentMethod =
 export type PaymentPlatform = "web" | "mobile";
 
 export interface InitiatePaymentPayload {
-  bookingId: string;
+  invoiceId: string;
   method: PaymentMethod;
   platform?: PaymentPlatform;
   payerAccount?: string;
@@ -67,6 +67,25 @@ function buildCheckoutUrl(payload: {
   return `${base}${P.CHECKOUT}?${params.toString()}`;
 }
 
+/**
+ * Checkout fallback keyed by invoice id — matches `GET /payments/checkout`,
+ * which reads `invoiceId` (billing is invoice-centric; there is no
+ * `bookingId` param on that route).
+ */
+function buildCheckoutUrlForInvoice(payload: {
+  invoiceId: string;
+  method: PaymentMethod;
+  platform?: PaymentPlatform;
+}): string {
+  const base = API_BASE_URL.replace(/\/$/, "");
+  const params = new URLSearchParams({
+    invoiceId: payload.invoiceId,
+    method: payload.method,
+    platform: payload.platform ?? "web",
+  });
+  return `${base}${P.CHECKOUT}?${params.toString()}`;
+}
+
 export const paymentsService = {
   initiate: async (
     payload: InitiatePaymentPayload,
@@ -84,4 +103,5 @@ export const paymentsService = {
   },
 
   checkoutUrl: buildCheckoutUrl,
+  checkoutUrlForInvoice: buildCheckoutUrlForInvoice,
 };