diff --git a/frontend/src/__tests__/PaymentRedirect.spec.ts b/frontend/src/__tests__/PaymentRedirect.spec.ts
index b13a395..dad5ea9 100644
--- a/frontend/src/__tests__/PaymentRedirect.spec.ts
+++ b/frontend/src/__tests__/PaymentRedirect.spec.ts
@@ -112,6 +112,16 @@ describe('PaymentRedirect', () => {
       expect(wrapper.find('.payment__qr-img').exists()).toBe(true)
     })
     expect(mockToDataURL).toHaveBeenCalledTimes(1)
+    // Regression guard: the QR must use a spec-compliant 4-module quiet zone
+    // and pure black-on-white so the Swish app can scan it off a screen.
+    expect(mockToDataURL).toHaveBeenCalledWith(
+      expect.stringContaining('app.swish.nu'),
+      expect.objectContaining({
+        margin: 4,
+        errorCorrectionLevel: 'M',
+        color: { dark: '#000000', light: '#ffffff' },
+      }),
+    )
   })
 
   it('renders a Swish payment link', async () => {
diff --git a/frontend/src/__tests__/payment.spec.ts b/frontend/src/__tests__/payment.spec.ts
new file mode 100644
index 0000000..fd1cd25
--- /dev/null
+++ b/frontend/src/__tests__/payment.spec.ts
@@ -0,0 +1,52 @@
+import { describe, it, expect } from 'vitest'
+import { buildSwishPaymentUrl } from '@/api/payment'
+
+describe('buildSwishPaymentUrl', () => {
+  it('normalises Swedish national format to international', () => {
+    expect(buildSwishPaymentUrl('0701234567', 49, 'test')).toContain(
+      'sw=46701234567',
+    )
+  })
+
+  it('strips a leading + from international format', () => {
+    const url = buildSwishPaymentUrl('+46701234567', 49, 'test')
+    expect(url).toContain('sw=46701234567')
+    expect(url).not.toContain('sw=%2B')
+    expect(url).not.toContain('sw=+')
+  })
+
+  it('leaves already-international numbers unchanged', () => {
+    expect(buildSwishPaymentUrl('46701234567', 49, 'test')).toContain(
+      'sw=46701234567',
+    )
+  })
+
+  it('leaves Swish Business numbers (123…) unchanged', () => {
+    expect(buildSwishPaymentUrl('1234567890', 49, 'test')).toContain(
+      'sw=1234567890',
+    )
+  })
+
+  it('strips whitespace from the number', () => {
+    expect(buildSwishPaymentUrl('070 123 45 67', 49, 'test')).toContain(
+      'sw=46701234567',
+    )
+  })
+
+  it('includes the amount with two decimal places in amt', () => {
+    expect(buildSwishPaymentUrl('0701234567', 49, 'test')).toContain(
+      'amt=49.00',
+    )
+  })
+
+  it('URL-encodes the message in the msg parameter', () => {
+    const url = buildSwishPaymentUrl('0701234567', 49, 'ABC 123')
+    expect(url).toContain('msg=ABC+123')
+  })
+
+  it('uses the correct Swish C2B base URL', () => {
+    expect(buildSwishPaymentUrl('0701234567', 49, 'test')).toContain(
+      'https://app.swish.nu/1/p/sw/?',
+    )
+  })
+})
diff --git a/frontend/src/api/payment.ts b/frontend/src/api/payment.ts
index 7d930e6..7a48541 100644
--- a/frontend/src/api/payment.ts
+++ b/frontend/src/api/payment.ts
@@ -48,9 +48,12 @@ export function buildSwishPaymentUrl(
  * - 123… (Swish Business number) → unchanged
  * - 46… (already international)  → unchanged
  * - 0… (Swedish national format) → 46 + rest without leading 0
+ * - +46… (international with plus) → 46… (the plus is stripped first)
  */
 function normalizeSwishNumber(number: string): string {
-  const trimmed = number.replace(/\s/g, '')
+  // Strip whitespace and a leading "+": a number stored as "+46 70 …" would
+  // otherwise miss every prefix check and leak a "+" into the `sw` param.
+  const trimmed = number.replace(/[\s+]/g, '')
   if (trimmed.startsWith('123')) return trimmed
   if (trimmed.startsWith('46')) return trimmed
   if (trimmed.startsWith('0')) return '46' + trimmed.slice(1)
diff --git a/frontend/src/pages/PaymentRedirect.vue b/frontend/src/pages/PaymentRedirect.vue
index d85fcaa..059a3a8 100644
--- a/frontend/src/pages/PaymentRedirect.vue
+++ b/frontend/src/pages/PaymentRedirect.vue
@@ -27,16 +27,30 @@ onMounted(async () => {
     const info = await fetchSwishInfo()
     swishNumber.value = info.number
     swishAmount.value = info.amount
+  } catch {
+    error.value = 'Kunde inte ladda betalningsinformation. Försök igen senare.'
+    return
+  }
 
+  // QR generation is best-effort and isolated from fetchSwishInfo: if the QR
+  // library throws, the Swish payment link and manual fallback still render
+  // instead of surfacing a misleading "could not load payment info" error.
+  try {
     if (swishPaymentUrl.value) {
       qrDataUrl.value = await QRCode.toDataURL(swishPaymentUrl.value, {
-        width: 224,
-        margin: 2,
-        color: { dark: '#111827', light: '#ffffff' },
+        // Swish requires a reliably scannable black-on-white QR. The previous
+        // settings (margin 2, #111827, 224px) produced a 2-module quiet zone
+        // — half the QR spec minimum — which the Swish app's scanner fails to
+        // read when scanning off a screen. Use the spec-compliant 4-module
+        // quiet zone, pure black, and larger modules.
+        width: 288,
+        margin: 4,
+        errorCorrectionLevel: 'M',
+        color: { dark: '#000000', light: '#ffffff' },
       })
     }
   } catch {
-    error.value = 'Kunde inte ladda betalningsinformation. Försök igen senare.'
+    // ignored: payment link + manual fallback remain usable
   }
 })
 
@@ -239,8 +253,8 @@ async function confirmPayment() {
 }
 
 .payment__qr-img {
-  width: 224px;
-  height: 224px;
+  width: 288px;
+  height: 288px;
   border-radius: var(--radius-md);
   margin: 0 auto var(--space-sm);
 }