No error message is returned for a failed generic messenger call

Description

If I set up a generic messenger and it returns a status code outside of 200-299 range, I'd expect some kind of notification. But it appears that the error message is swallowed.

Affects versions

1.32.1

Steps to reproduce

1. Set up a user and tenant with SMS MFA.
2. Create a generic messenger. Have the URL be https://httpbin.org/status/401 which always returns a 401.
3. Configure the tenant to use the generic messenger.
4. Open up an incognito window and log in as the user with MFA enabled.
5. When you get to the MFA screen, there is no notice that the call to the generic messenger failed.

Expected behavior

I'd like to see:

• an event log entry (possibly gated by a 'debug' setting on the Generic messenger).
• some kind of indication to the user in the UX that the message failed to send.

Related

• Add debug/error event logging to generic messenger and other enhancements #1574

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Additional context

We should update the docs added in this PR with information about how the error message is displayed when the message receiver fails to return a 200: