Handle 422 errors from checkout API

[seer-by-sentry]

👋 Hi there! This PR was automatically generated by Autofix 🤖

This fix was triggered by [email protected].

Fixes ANDROID-10. The issue was that: Backend inventory shortage caused a 500 error, triggering the Android app to intentionally throw a 'Failed to init delivery workflow' exception.

• Display a user-friendly error message when the checkout API returns a 422 status code, indicating an item is out of stock or another validation error.
• Parse the error message from the JSON response body.
• Handle generic errors with a general error message.

If you have any questions or feedback for the Sentry team about this fix, please email [email protected] with the Run ID: 34730.