When we tried to add the account to managed users, we got the error "Cannot add new users. Please try again." in the Users & Groups tool. 

The e-mail address that we want to add is formerly associated with a personal account, but he deleted his personal account in January 2024 in order not to affect registering to the business account.

FYI, we tried the method proposed in the following thread (https://support.box.com/hc/en-us/community/posts/25740552529683-Email-already-used-in-a-Box-account-but-not-associated-with-an-enterprise ), but it did not resolve our problem.

We would like to add his e-mail address to managed users as soon as possible.
We would appreciate it if you could help us to solve this problem.