Amazon Rekognition - Unexpected Error from DeleteUsersAsync method call

Question

Hello,
I am trying to utilize the [DeleteUser](https://docs.aws.amazon.com/rekognition/latest/APIReference/API_DeleteUser.html) in C# AWSSSO.Rekognition.
When I pass in the CollectionId and UserId of a valid User, I am able to Delete the User without issue. 
When I pass in a valid CollectionId, but a UserId of a User that does not exist, I get an InvalidParameterException instead of the expected ResourceNotFoundException.

For both the Users that exist, and the User that does not, I am utilizing a string GUID, which falls within allowed Input Param pattern. I am looking for a way to differentiate whether the User does not exist, but am getting this error every time instead.

The documentation above lists both InvalidParameterException and ResourceNotFoundException as valid exceptions returned by the method.

re:Post Agent · Answer

When using the DeleteUser operation in Amazon Rekognition, you're encountering an InvalidParameterException when attempting to delete a user that doesn't exist, rather than the ResourceNotFoundException you expected.

This behavior appears to be inconsistent with what you might expect based on the API documentation. The InvalidParameterException indicates that an input parameter violated a constraint, which suggests that the system is treating the non-existent UserId as an invalid parameter rather than a missing resource.

To work around this issue, you could:

1. Handle both InvalidParameterException and ResourceNotFoundException in your code as potential indicators that the user doesn't exist.

2. Before attempting to delete a user, you could first verify if the user exists using another API call (such as ListUsers if available).

3. Implement error handling that treats the InvalidParameterException in this specific context as an indication that the user doesn't exist.

If you need to specifically differentiate between a user that doesn't exist and other parameter validation issues, you may want to examine the error message details within the InvalidParameterException to see if it provides more specific information about why the parameter was considered invalid.  
**Sources**  
[Deleting a user - Amazon Rekognition](https://docs.aws.amazon.com/rekognition/latest/dg/delete-user.html)  
[DeleteUser - Amazon Rekognition](https://docs.aws.amazon.com/rekognition/latest/APIReference/API_DeleteUser.html)

Amazon Rekognition - Unexpected Error from DeleteUsersAsync method call

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