The best way to pay with Bitcoin is to use the app BitPay.
You need bitcoins in it. How to buy can differ by region. Coinbase should have worldwide coverage; however if you want an alternative, Google: "how to buy Bitcoin", to get options in your region. Click this link to Google it: https://lmgtfy.com/?q=buy+bitcoin
You have to send the Bitcoins to your own BitPay (BTC) wallet.
After the payment is confirmed, you can proceed to order and scan the QR code with your BitPay app to easily make the Bitcoin payment.