diff --git a/backend/src/modules/order/services/OrderService.ts b/backend/src/modules/order/services/OrderService.ts
index 882930f..0edb1bb 100644
--- a/backend/src/modules/order/services/OrderService.ts
+++ b/backend/src/modules/order/services/OrderService.ts
@@ -260,10 +260,6 @@ export class OrderService {
             amountFiat: deliveryCost
         });
 
-        if (!shippingInvoice) {
-            throw new InternalServerErrorException('Failed to issue shipping invoice');
-        }
-
         await this.orderRepo.update(orderId, {
             shippingInvoice: { id: shippingInvoice.id },
             quotedAt
diff --git a/backend/src/modules/payment/services/InvoiceService.spec.ts b/backend/src/modules/payment/services/InvoiceService.spec.ts
index 3b959ab..e187ddd 100644
--- a/backend/src/modules/payment/services/InvoiceService.spec.ts
+++ b/backend/src/modules/payment/services/InvoiceService.spec.ts
@@ -1,4 +1,4 @@
-import { Logger, ServiceUnavailableException } from '@nestjs/common';
+import { Logger, InternalServerErrorException, ServiceUnavailableException } from '@nestjs/common';
 import type { ConfigService } from '@nestjs/config';
 import type { Repository } from 'typeorm';
 import type { ElectrumWalletRpcClient } from '../../bitcoinWallet/services/ElectrumWalletRpcClient';
@@ -301,4 +301,15 @@ describe('InvoiceService', () => {
             )
         );
     });
+
+    it('throws for unsupported payment methods', async () => {
+        await expect(
+            service.issueInvoice({
+                paymentMethod: 'eth' as PaymentMethod,
+                reason: InvoiceReason.Checkout,
+                contextId: 'session-uuid',
+                amountFiat: 15
+            })
+        ).rejects.toThrow(new InternalServerErrorException('Unsupported payment method: eth'));
+    });
 });
diff --git a/backend/src/modules/payment/services/InvoiceService.ts b/backend/src/modules/payment/services/InvoiceService.ts
index 1c5fcd0..5a4f0fb 100644
--- a/backend/src/modules/payment/services/InvoiceService.ts
+++ b/backend/src/modules/payment/services/InvoiceService.ts
@@ -1,4 +1,4 @@
-import { Injectable, Logger, ServiceUnavailableException } from '@nestjs/common';
+import { Injectable, InternalServerErrorException, Logger, ServiceUnavailableException } from '@nestjs/common';
 import { InjectRepository } from '@nestjs/typeorm';
 import { ConfigService } from '@nestjs/config';
 import { Repository } from 'typeorm';
@@ -32,12 +32,14 @@ export class InvoiceService {
         private readonly exchangeRateService: ExchangeRateService
     ) {}
 
-    async issueInvoice(data: IssueInvoiceData): Promise<Invoice | undefined> {
+    async issueInvoice(data: IssueInvoiceData): Promise<Invoice> {
         switch (data.paymentMethod) {
             case PaymentMethod.Xmr:
                 return this.issueXmrInvoice(data);
             case PaymentMethod.Btc:
                 return this.issueBtcInvoice(data);
+            default:
+                throw new InternalServerErrorException(`Unsupported payment method: ${String(data.paymentMethod)}`);
         }
     }