I don't understand what actually you want to explain but it seems that you want to pay BTC directly to a payment address?
If the payment address you talking about is the address of BTC he will receive also BTC there are wallets that automatically calculate it in USD.

But if you talking about BTC then you are going to buy something online with your BTC through a debit card with a BTC balance then there are still available online like Coinbase card you can find it here https://www.coinbase.com/card you can spend your crypto with this card and sellers who paid with Coinbase card will receive USD.

Another option that I know of is https://paywithmoon.com/ where you can able to deposit supported crypto and generate a VCC that you can use to buy anything online or to pay someone that accepts VCC.