A payment URI is a request for payment that many wallets can generate. URIs define a target address, an amount and may include a notification for the sender such as the order number. These can be scanned like a QR code or copied into the send field of a wallet. One click on the payment URI opens the wallet with the pre-formulated transaction.
The payment service provider BitPay uses the payment protocol. This enables BitPay to set fees for a transaction and transfer this amount to the miner itself. In this way, BitPay can increase the success rate of its payments. This payment method is used in the same way as the URI: you can scan it in, click the link or copy it into a wallet. In any case, not all wallets support the payment protocol.