Auto-generated Site_Url cannot handle every username
If username has e.g. dashes then it shows error ‘site name can only have lowercase letters and numbers’ and the user does not know what went wrong, because site_url is hidden. Or if it’s only numbers then it says ‘must have letters’ but creates the customer anyway. And going back in a multistep and adding a letter still gives the error at the end. So user is stuck.