Try to create a test account with name 'test11' and it returns nothing in client side.
If create in the admin area, it returns the following.
Error: Cannot add the group administrator account. [HTTP error code 409 ("409 Need to specify explicitly that user should be created using an existing identity")]
Manually changed the account name to something else, and it went alright.
We cannot reproduce the issue on our side. Could you please provide logs we requested earlier?
Backup administrator account creation may fail in case of another account with the same login already exists in our cloud. And WHMCS doesn't allow to validate the login in store. In this case, client can add the account from client area later.