Reply to @belengarcia: well an invoice and a receipt in some ways are the same thing when coming from Fiverr. You get an “invoice” if you will when you order the job along with the payment receipt that could possible be enough for some things. So I was thinking of that email notification as an “invoice” but I have read a few times in here something about Fiverr can provide an invoices if request for the month or something like that.
Here in the US as long as the email states what it is, and confirmation of payment, an email could be an invoice and prove the contract in most cases in court. But it may be different in the EU, which is interesting in general when it comes to Fiverr or any other site of people working for other countries.