Unable to confirm user in Zoho CRM

We try to add a new user to zoho crm but every time we send him a (re)invite email, he cannot log in the system, he receives the notification that his account is disabled.

In Zoho CRM, the user has the status Not Confirmed. In CRM, we can assign accounts to him. but he is unable to log in.

We reviewed all information about this problem but couldn't find a solution. We already tried the following:

1. Enabling the user in the superadmin control panel

2. Deleting other mail address related the same account

3. Deactivating the user and reactivating him again.

Can somebody please help us? It is quite urgent that he gets access to zoho crm.

Thanks!