I've created a new domain in my GSuite account so there are two domains in there (not an alias but an actual new domain). There is an existing user 'email@example.com' and I'm trying to add 'firstname.lastname@example.org' however it is telling me that the username already exists and to either transfer my data or to rename the user. Granted the username is the same but the domains are different, how do I get around this??
Ok for anyone having a similar issue - I've figured it out, it seems that the email@example.com had already been setup under a different account altogether and that's where the conflict was coming from, not the GSuite account.
I had this same issue and the fix for me was to choose the new domain from the drop-down first and then type in the username.