Support is currently swamped. There’s a good chance they haven’t read your ticket, yet.

I talked with leafo he told me that some billing should be after I made first payout, I will make in 2 days and we will see is there informations that I need. If not I will have to also stop selling anything on Itch io. I don't get it why I don't have here any information about here: https://eintaxid.com/ ? The company have other name than itch corp? I don't know what types of bussines are in US but about itch corp you can't find anything.

Just duplicating my reply:

If you have received a payout form us then you will find a link to generate a receipt of payment on that payout’s page in your dashboard. It includes a breakdown and all relevant information (VAT number, address, etc.). Hope that helps!

For that developer we provided them with instructions awhile back but they don’t appear to have updated their page or have an interest in updating it.