I have faced the same problem that you are talking about. when I was trying to add my PayPal account on Fiverr. when I have clicked on “PayPal Account” button, first time Fiverr ask me to put a 4 digit code on the popup, but I could not verify my mobile number because my mobile display was broken, and then I tried to get the code by a call, and also I could not have received the call too.
The third time I saw the same message that screenshot you have uploaded.
I eagerly suggest you, knock on Fiverr support them they will fix the problem as soon as they received your message.