You don’t need that form. You also should get a new accountant.
If you live in the U.S. and earned money, even from a company that is not based in the U.S. you just go ahead and pay taxes on your income.
There is no reason to tell anyone that fiverr is not based in the U.S. as you pay the same taxes no matter where it is.
I was just reading about that form so if you are a foreigner in the U.S. then you may need it, I’m not sure:
Purpose of Form
This form is used by foreign entities to document their
status for purposes of chapter 3 and chapter 4, as well as
for certain other Code provisions as described later in
Foreign persons are subject to U.S. tax at a 30% rate
(the foreign-person withholding rate) on income they
receive from U.S. sources that consists of:
Interest (including certain original issue discount (OID));
Compensation for, or in expectation of, services
Substitute payments in a securities lending transaction;
Other fixed or determinable annual or periodical gains,
profits, or income.
So you may indeed need that form. It is my understanding that since fiverr has many offices located in the U.S. then that qualifies them as a U.S. company even if their headquarters is in another country as far as being a U.S. company for tax purposes.
If you have contacted customer support than I have no answer for how to get that form.
I think you need to pay tax to the U.S. government at a 30% rate if you earned over $600.
I don’t see that you have any reviews and you just joined in December of 2016 so you may not have earned enough to worry about taxes.