diff --git a/app/routes/api.public.payment-info.tsx b/app/routes/api.public.payment-info.tsx
new file mode 100644
index 0000000..e46fb91
--- /dev/null
+++ b/app/routes/api.public.payment-info.tsx
@@ -0,0 +1,165 @@
+import type { LoaderFunctionArgs } from "react-router";
+import { authenticate, unauthenticated } from "../shopify.server";
+import db from "../db.server";
+import { buildGiroCodeDataUrl } from "../services/invoice/girocode";
+import { formatMoney, formatDate, addDays } from "../services/invoice/format";
+import { getStrings, pickLanguage } from "../services/invoice/i18n";
+
+/**
+ * Public endpoint consumed by the checkout / thank-you UI extension to fetch
+ * payment instructions (GiroCode + bank details) for an order.
+ *
+ * Auth: validated Shopify checkout session token (via `authenticate.public.checkout`).
+ * The shop domain is derived from `sessionToken.dest`; the order id is read
+ * from the `?orderId=` query parameter (numeric or GID, both accepted).
+ *
+ * Returns:
+ *   { showPaymentInstructions: boolean, payload?: { ... } }
+ *
+ * `payload` is only populated when:
+ *   - the order has at least one transaction processed by a manual payment
+ *     gateway (Shopify's `manualPaymentGateway` flag), and
+ *   - the shop has an IBAN configured.
+ */
+export const loader = async ({ request }: LoaderFunctionArgs) => {
+  const { sessionToken, cors } = await authenticate.public.checkout(request);
+  const shop = (sessionToken.dest ?? "").toString().replace(/^https?:\/\//, "");
+  if (!shop) {
+    return cors(Response.json({ showPaymentInstructions: false, error: "no-shop" }, { status: 400 }));
+  }
+
+  const url = new URL(request.url);
+  const orderIdRaw = url.searchParams.get("orderId");
+  if (!orderIdRaw) {
+    return cors(Response.json({ showPaymentInstructions: false, error: "no-order-id" }, { status: 400 }));
+  }
+  const orderGid = orderIdRaw.startsWith("gid://")
+    ? orderIdRaw
+    : `gid://shopify/Order/${orderIdRaw.replace(/[^0-9]/g, "")}`;
+
+  const settings = await db.shopSettings.findUnique({ where: { shopDomain: shop } });
+  if (!settings?.iban || !settings.giroCodeEnabled) {
+    // No bank details / GiroCode disabled — nothing to render.
+    return cors(Response.json({ showPaymentInstructions: false, reason: "no-iban-or-disabled" }));
+  }
+
+  const { admin } = await unauthenticated.admin(shop);
+  let orderInfo: OrderInfo | null = null;
+  try {
+    orderInfo = await fetchOrderInfo(admin, orderGid);
+  } catch (err) {
+    console.warn(`payment-info: failed to load order ${orderGid} for ${shop}:`, err);
+    return cors(Response.json({ showPaymentInstructions: false, error: "order-load-failed" }, { status: 502 }));
+  }
+  if (!orderInfo || !orderInfo.isManual) {
+    return cors(Response.json({ showPaymentInstructions: false, reason: "not-manual-payment" }));
+  }
+
+  const language = pickLanguage(orderInfo.customerLocale ?? settings.defaultLanguage);
+  const t = getStrings(language);
+
+  // Outstanding amount: prefer totalOutstanding (set by Shopify for unpaid),
+  // fall back to totalPrice when zero.
+  const amount = orderInfo.outstandingAmount > 0 ? orderInfo.outstandingAmount : orderInfo.totalAmount;
+  const remittance = orderInfo.orderName || orderGid.split("/").pop() || "";
+
+  const giroCodeDataUrl = await buildGiroCodeDataUrl({
+    beneficiaryName: [settings.companyName, settings.legalForm].filter(Boolean).join(" "),
+    iban: settings.iban,
+    bic: settings.bic,
+    amount,
+    currency: orderInfo.currency,
+    remittance,
+  });
+
+  const dueDate = settings.paymentTermDays > 0
+    ? addDays(new Date(), settings.paymentTermDays)
+    : null;
+
+  return cors(
+    Response.json({
+      showPaymentInstructions: true,
+      payload: {
+        language,
+        heading: t.giroCodeCaption,
+        giroCodeDataUrl,
+        recipient: [settings.companyName, settings.legalForm].filter(Boolean).join(" "),
+        bankName: settings.bankName,
+        iban: settings.iban,
+        bic: settings.bic,
+        amountFormatted: formatMoney(amount, orderInfo.currency, language),
+        reference: remittance,
+        dueDateFormatted: dueDate ? formatDate(dueDate, language) : null,
+        instructions: dueDate
+          ? t.paymentTerms(settings.paymentTermDays, formatDate(dueDate, language))
+          : t.paymentTermsImmediate,
+        labels: {
+          recipient: t.recipientLabel,
+          bank: t.bankLabel,
+          iban: t.ibanLabel,
+          bic: t.bicLabel,
+          amount: t.amountLabel,
+          reference: t.referenceLabel,
+        },
+      },
+    }),
+  );
+};
+
+interface OrderInfo {
+  isManual: boolean;
+  totalAmount: number;
+  outstandingAmount: number;
+  currency: string;
+  orderName: string;
+  customerLocale?: string;
+}
+
+async function fetchOrderInfo(
+  admin: { graphql: (q: string, opts?: { variables?: Record<string, unknown> }) => Promise<Response> },
+  orderGid: string,
+): Promise<OrderInfo | null> {
+  const res = await admin.graphql(
+    `#graphql
+    query OrderPaymentInfo($id: ID!) {
+      order(id: $id) {
+        name
+        currencyCode
+        customerLocale
+        totalPriceSet { shopMoney { amount } }
+        totalOutstandingSet { shopMoney { amount } }
+        transactions(first: 20) {
+          status
+          manualPaymentGateway
+        }
+      }
+    }`,
+    { variables: { id: orderGid } },
+  );
+  const json = (await res.json()) as {
+    data?: {
+      order?: {
+        name?: string;
+        currencyCode?: string;
+        customerLocale?: string | null;
+        totalPriceSet?: { shopMoney: { amount: string } };
+        totalOutstandingSet?: { shopMoney: { amount: string } };
+        transactions?: Array<{ status?: string; manualPaymentGateway?: boolean }>;
+      } | null;
+    };
+  };
+  const o = json.data?.order;
+  if (!o) return null;
+  const txs = o.transactions ?? [];
+  const isManual = txs.some(
+    (t) => t.manualPaymentGateway === true && t.status !== "FAILURE" && t.status !== "ERROR",
+  );
+  return {
+    isManual,
+    totalAmount: parseFloat(o.totalPriceSet?.shopMoney.amount ?? "0"),
+    outstandingAmount: parseFloat(o.totalOutstandingSet?.shopMoney.amount ?? "0"),
+    currency: o.currencyCode ?? "EUR",
+    orderName: o.name ?? "",
+    customerLocale: o.customerLocale ?? undefined,
+  };
+}
diff --git a/extensions/invoice-thank-you-payment/package.json b/extensions/invoice-thank-you-payment/package.json
new file mode 100644
index 0000000..2263100
--- /dev/null
+++ b/extensions/invoice-thank-you-payment/package.json
@@ -0,0 +1,11 @@
+{
+  "name": "invoice-thank-you-payment",
+  "version": "1.0.0",
+  "private": true,
+  "devDependencies": {
+    "@preact/signals": "^1.3.0",
+    "@shopify/ui-extensions": "^2026.1.0",
+    "preact": "^10.22.0",
+    "typescript": "^5.6.0"
+  }
+}
diff --git a/extensions/invoice-thank-you-payment/shopify.d.ts b/extensions/invoice-thank-you-payment/shopify.d.ts
new file mode 100644
index 0000000..cca04c5
--- /dev/null
+++ b/extensions/invoice-thank-you-payment/shopify.d.ts
@@ -0,0 +1,7 @@
+import '@shopify/ui-extensions';
+
+//@ts-ignore
+declare module './src/Checkout.tsx' {
+  const shopify: import('@shopify/ui-extensions/purchase.thank-you.block.render').Api;
+  const globalThis: { shopify: typeof shopify };
+}
diff --git a/extensions/invoice-thank-you-payment/shopify.extension.toml b/extensions/invoice-thank-you-payment/shopify.extension.toml
new file mode 100644
index 0000000..7a05c81
--- /dev/null
+++ b/extensions/invoice-thank-you-payment/shopify.extension.toml
@@ -0,0 +1,15 @@
+api_version = "2026-01"
+
+[[extensions]]
+name = "Invoice payment instructions"
+handle = "invoice-thank-you-payment"
+type = "ui_extension"
+uid = "linumiq-invoice-thank-you-payment"
+
+  [[extensions.targeting]]
+  target = "purchase.thank-you.block.render"
+  module = "./src/Checkout.tsx"
+
+  [extensions.capabilities]
+  network_access = true
+  api_access = false
diff --git a/extensions/invoice-thank-you-payment/src/Checkout.tsx b/extensions/invoice-thank-you-payment/src/Checkout.tsx
new file mode 100644
index 0000000..a61ca7a
--- /dev/null
+++ b/extensions/invoice-thank-you-payment/src/Checkout.tsx
@@ -0,0 +1,103 @@
+import "@shopify/ui-extensions/preact";
+import { render } from "preact";
+import { useEffect, useState } from "preact/hooks";
+
+const APP_URL = "https://invoice-app.linumiq.com";
+
+interface PaymentInstructions {
+  language: "de" | "en";
+  heading: string;
+  giroCodeDataUrl: string;
+  recipient: string;
+  bankName: string;
+  iban: string;
+  bic: string;
+  amountFormatted: string;
+  reference: string;
+  dueDateFormatted: string | null;
+  instructions: string;
+  labels: {
+    recipient: string;
+    bank: string;
+    iban: string;
+    bic: string;
+    amount: string;
+    reference: string;
+  };
+}
+
+export default async () => {
+  render(<Extension />, document.body);
+};
+
+function Extension() {
+  const shopify = (globalThis as any).shopify;
+  const [data, setData] = useState<PaymentInstructions | null>(null);
+  const [done, setDone] = useState(false);
+
+  useEffect(() => {
+    let cancelled = false;
+    async function load() {
+      try {
+        const orderId: string | undefined = shopify?.orderConfirmation?.value?.order?.id;
+        if (!orderId) {
+          setDone(true);
+          return;
+        }
+        const token: string = await shopify.sessionToken.get();
+        const res = await fetch(
+          `${APP_URL}/api/public/payment-info?orderId=${encodeURIComponent(orderId)}`,
+          { headers: { Authorization: `Bearer ${token}` } },
+        );
+        if (!res.ok) {
+          setDone(true);
+          return;
+        }
+        const json = (await res.json()) as {
+          showPaymentInstructions: boolean;
+          payload?: PaymentInstructions;
+        };
+        if (cancelled) return;
+        if (json.showPaymentInstructions && json.payload) {
+          setData(json.payload);
+        }
+      } catch {
+        // ignore — render nothing on error
+      } finally {
+        if (!cancelled) setDone(true);
+      }
+    }
+    load();
+    return () => {
+      cancelled = true;
+    };
+  }, []);
+
+  if (!done) {
+    return <s-skeleton-paragraph />;
+  }
+  if (!data) {
+    return null;
+  }
+
+  return (
+    <s-section heading={data.heading}>
+      <s-paragraph>{data.instructions}</s-paragraph>
+      <s-stack direction="inline" gap="base" align-items="start">
+        <s-image src={data.giroCodeDataUrl} alt="GiroCode" />
+        <s-stack direction="block" gap="small-200">
+          <s-text>{data.labels.recipient}: {data.recipient}</s-text>
+          {data.bankName ? (
+            <s-text>{data.labels.bank}: {data.bankName}</s-text>
+          ) : null}
+          <s-text>{data.labels.iban}: {data.iban}</s-text>
+          {data.bic ? (
+            <s-text>{data.labels.bic}: {data.bic}</s-text>
+          ) : null}
+          <s-text>{data.labels.amount}: {data.amountFormatted}</s-text>
+          <s-text>{data.labels.reference}: {data.reference}</s-text>
+        </s-stack>
+      </s-stack>
+    </s-section>
+  );
+}
diff --git a/extensions/invoice-thank-you-payment/tsconfig.json b/extensions/invoice-thank-you-payment/tsconfig.json
new file mode 100644
index 0000000..84713c4
--- /dev/null
+++ b/extensions/invoice-thank-you-payment/tsconfig.json
@@ -0,0 +1,18 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "Bundler",
+    "lib": ["DOM", "DOM.Iterable", "ES2022"],
+    "jsx": "react-jsx",
+    "jsxImportSource": "preact",
+    "strict": true,
+    "skipLibCheck": true,
+    "isolatedModules": true,
+    "noEmit": true,
+    "resolveJsonModule": true,
+    "allowSyntheticDefaultImports": true,
+    "esModuleInterop": true
+  },
+  "include": ["src/**/*"]
+}
diff --git a/package-lock.json b/package-lock.json
index 199471e..4634db4 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -77,6 +77,15 @@
         "typescript": "^5.6.0"
       }
     },
+    "extensions/invoice-thank-you-payment": {
+      "version": "1.0.0",
+      "devDependencies": {
+        "@preact/signals": "^1.3.0",
+        "@shopify/ui-extensions": "^2026.1.0",
+        "preact": "^10.22.0",
+        "typescript": "^5.6.0"
+      }
+    },
     "node_modules/@ardatan/relay-compiler": {
       "version": "13.0.1",
       "resolved": "https://registry.npmjs.org/@ardatan/relay-compiler/-/relay-compiler-13.0.1.tgz",
@@ -3129,6 +3138,34 @@
         "url": "https://opencollective.com/parcel"
       }
     },
+    "node_modules/@preact/signals": {
+      "version": "1.3.4",
+      "resolved": "https://registry.npmjs.org/@preact/signals/-/signals-1.3.4.tgz",
+      "integrity": "sha512-TPMkStdT0QpSc8FpB63aOwXoSiZyIrPsP9Uj347KopdS6olZdAYeeird/5FZv/M1Yc1ge5qstub2o8VDbvkT4g==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@preact/signals-core": "^1.7.0"
+      },
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/preact"
+      },
+      "peerDependencies": {
+        "preact": "10.x"
+      }
+    },
+    "node_modules/@preact/signals-core": {
+      "version": "1.14.1",
+      "resolved": "https://registry.npmjs.org/@preact/signals-core/-/signals-core-1.14.1.tgz",
+      "integrity": "sha512-vxPpfXqrwUe9lpjqfYNjAF/0RF/eFGeLgdJzdmIIZjpOnTmGmAB4BjWone562mJGMRP4frU6iZ6ei3PDsu52Ng==",
+      "dev": true,
+      "license": "MIT",
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/preact"
+      }
+    },
     "node_modules/@prisma/client": {
       "version": "6.19.3",
       "resolved": "https://registry.npmjs.org/@prisma/client/-/client-6.19.3.tgz",
@@ -9242,6 +9279,10 @@
       "resolved": "extensions/invoice-order-block",
       "link": true
     },
+    "node_modules/invoice-thank-you-payment": {
+      "resolved": "extensions/invoice-thank-you-payment",
+      "link": true
+    },
     "node_modules/ipaddr.js": {
       "version": "1.9.1",
       "resolved": "https://registry.npmjs.org/ipaddr.js/-/ipaddr.js-1.9.1.tgz",