Why does it say someone 'cannot receive payments sent with Apple Pay at this time'

iOS 11.2 introduces Apple Pay Cash -- a peer-to-peer money transferring service from Apple. Apple Pay Cash allows users to send and receive payments through the Messages app on iOS devices. Payments can only be sent to other iOS users with a device running iOS 11.2 or later. The person receiving the money or payment request also needs to have Apple Pay Cash setup on their device. If you try to send cash or request a payment to someone who does not meet these requirements you will receive the 'cannot receive payments sent with Apple Pay at this time' message.