Problem description
While reviewing PR #329 and based on this comment, think maybe we need some actions with regards to the errors documented in the event notification artifact.

1. Should we remove 500, 503 errors from the artifact (i.e. we assume any server exception is implicitly managed by the API consumer, in the same fashion as we do for Telco Operator)? And therefore align it in API Design guidelines?

2. As in artifact are documented 400, 401, 403, 410, 429, should we considered all of them as mandatory? And therefore align it in API Design guidelines?

Parent Issue: #273

Expected behavior
Based on the output discussion.

Initially the proposal would be:

• Remove Errors 500, 503 from the artifact. Align in API Design Guidelines
• Consider Errors 410 and 429 as mandatory for event notifications. Align in API Design Guidelines

Alternative solution
Not evaluated

Additional context
Alignment of Errors the CAMARA guidelines
Based on output I can generate a PR or take advantage of ongoing PR #329