Sure, in the US, you want to have those things to prove your expenses to the IRS, but it’s all pretty freeform. You could just document the ransomware payment process with screenshots, for example.
Besides, if you ask, I’m sure the ransomware group will send you a very professional-looking invoice and receipt.
Normally, you’d be going through an IR company anyway, who would invoice you and handle the payment process on your behalf.