A CloudOps engineer has an Amazon S3 bucket and a new AWS Lambda function.

The important clue is that the new Lambda function and its IAM role are already correctly configured. When S3 validates event notification configurations, it can validate not only the newly added destination but also existing destinations on the bucket. If the bucket already has a stale notification that points to a deleted Lambda function, deleted queue, deleted topic, or destination without the correct resource policy, the validation can fail with “Unable to validate the following destination configurations.” Option C would be plausible if the new Lambda permission were missing, but the question rules out a problem with the new function configuration. Option A is not the best cause because the error refers to destination validation, not a quota breach. Therefore, the stale existing event notification is the likely root cause.

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