The Fiverr account creation dialog bans spaces from user names. Most other sites with this odd limitation warn the user of restricted characters, either as part of the dialog text or as a popup when an invalid name is entered, but Fiverr does nothing but draw a red outline around the entry field when the submit button is clicked. Since most human names contain spaces, a reasonable but inexperienced user would have no way to guess what the problem is and might quit in frustration. You might want to either allow spaces or add descriptive error messages.
phasmafelis said: Since most human names contain spaces
That's not your name, but your nickname, so it's pretty normal you can't use spaces!
I think the OP’s remarks concerned Fiverr’s unwillingness or incapability in providing their users with information. Not just failing to explain error messages but lots of other issues like why Gigs get rejected, why Gallery pictures do not meet their standards.