I believe there may be an issue with mailbox delegation.

When I create a delegation from the Admin Console, it works correctly if I select Read permissions.

However, if I select Send As permission for the delegated user, I immediately receive the following error:

"The input passed is invalid"

Could you please check whether this is a bug or if there are additional requirements for granting "Send As" permissions through mailbox delegation?

My goal is to allow the delegated user to access and send emails from all aliases associated with the mailbox.