Crash when logon transaction returns HTTP 400 #661

Summary

During UI testing, a POST /api/logontransactions failure with HTTP 400 causes the application to crash instead of handling the error path gracefully.

Observed flow

• GET /health returns 200
• POST /connect/token for the service client returns 200
• GET /api/transactionmobileconfiguration/{deviceIdentifier} returns 200
• POST /connect/token for the mobile app user returns 200
• POST /api/logontransactions returns 400
• The application then crashes

Example trace

>>> POST /api/logontransactions
>>> REQUEST PAYLOAD {
  "application_version": "1.0.5",
  "device_identifier": "stagingmerchant1device",
  "transaction_date_time": "2026-08-20 13:06:32",
  "transaction_number": "1"
}
<<< 400 POST /api/logontransactions
<<< RESPONSE PAYLOAD <empty>

Expected

The app should surface a recoverable logon failure state or retry path.

Actual

The app crashes after the 400 response.

Notes

This was observed in the local UI test harness against the backend stub, so the failure appears to be in the app's handling of the error response rather than the test harness itself.