What could be the cause of the error messages for these customers?
The Lambda function reached its concurrency limit.
The Lambda function its Region limit for concurrency.
The company reached its API Gateway account limit for calls per second.
The company reached its API Gateway default per-method limit for calls per second.
Explanations:
The logs indicate that the Lambda function is never invoked, suggesting that the issue lies before invocation, not a concurrency limit.
Similar to option A, if the Lambda function was never invoked, it cannot have reached its Region limit for concurrency.
The company could have reached its API Gateway account limit for calls per second, leading to 429 errors, especially during peak usage.
While the per-method limit could be a factor, the problem seems to stem from an overall account limit rather than a specific method limit.