Where does “payer” come from?

payer (Middle French) comes from Old French paiier, from Medieval Latin pacare, from Latin pācāre, from Latin pāx, from Proto-Italic pāks, from Proto-Indo-European péh₂ḱ-s, from Proto-Indo-European peh₂ḱ- — to join, to attach; agreement, settlement.

payer (Middle French): to pay