Dears,
We have faced the below error when installing dynamics CRM on-premise version 9
Error| Install exception.System.Exception: Action Microsoft.Crm.Setup.Server.InstallConfigDatabaseAction failed. ---> Microsoft.Crm.CrmArgumentException: Invalid user name. Failed to validate username for given domain. Only existing domain usernames and email addresses are allowed ---> System.ArgumentException: Invalid user name. Failed to validate username for given domain. Only existing domain usernames and email addresses are allowed.