Unable to create a google workspace account

[Calixt]

Hi. i want to sign up for a google account to have aliases for my employees. But when I reach where I should write down my domain name it tells me it Is already used even though no one does. When I do the procedure and want to use the administrator email that doesn't end with Google.com, it says It is impossible because the email does not exist. I don't know what else to do. 
I need your help.

Thanks