For anyone facing the 429 error with type insufficient_quota, we solved it by specifying the Hard limit. Our configuration only specified the Soft limit, but it seems insufficient.
The missing max limit in the "Usage this month" progress bar on the "Usage" page was a hint of the problem.
I would consider this a bug because
- The Hard limit is not required.
- The Approved usage limit should work as the default hard limit.
I suspect a bug in the way the max limit is set.
I hope this could help someone else