What it is

It’s a tax on US purchases - explained here https://help.author.envato.com/hc/en-us/articles/360000471243-Tax-Information-Form-W-8-Requirements-for-non-US-Authors#royal

I am not a US citizen

you are from Moldova. according to US Tax Treaties required 0% tax.

But for getting this 0% tax facility you have to provide TAX information through settings=>tax information. When you complete your tax information, you must also provide Tax Identity Number, otherwise, Envato are required to deduct royalty withholding tax of 30% on your sales to US customers.

no you are not lol but u are a foreigner selling to us citizens so that the us governments taxes u every single time u sell to americans, according to the tax rate determined between your country and usa …