When you try to enter @ in the User Name field in app Manage Business Users, there is a message showing: only letters, numbers, periods, and underscores are allowed.
While you may find on your another tenant, it is allowed to enter @ (e.g. email address) in the User Name field.
The field UserName in Fiori App “Maintain Business Users” is only 40 chars long and should not be used for Email addresses as Email address can have a length of 241 chars. Email Address should be filled in the Workplace Address EMAIL field. In SAP IAS the customers can decide which fields should be used for logon. Email Address / User Alias (UserName) or UserAlias (UserName) only. Normally customers decide to use Email Address/UserAlias (UserName).
While there was a gap that it was possible to fill in e-mail address as user name via the automated upload/replication. As a result, to ensure consistency, for systems that already have existing entries containing the invalid characters, we switch off the check for the User Name field. While for new tenants, by default the check is switched on. (That's why you may find different behaviors on different tenants)
For the User Name field, please enter a name or ID that is identical with the login name of the same user in the on-premise identity provider.
UserName, e-mail address , KBA , BC-SRV-APS-IAM , Identity and Access Management , Problem