Issue Adding Users to Amazon Account – "This secondary user cannot be added" Error

Hi everyone,

I'm trying to add users to help manage my Amazon account, but I keep encountering the same error during the process:

Path:

User Permissions → User Management → Edit (user) → Edit User Permissions → Complete identity verification for United Kingdom → Finish verification

Error Message:

“This secondary user cannot be added to this account using this email address. Please use an alternative email address.”

I've tested several different email addresses, including company emails, but I always get the same result.

A few times, a form randomly appeared asking for personal information and ID verification for the user. I completed the form, but the same error still shows up afterward.

Has anyone else experienced this or know how to resolve it?

Thanks in advance for any help!