Person to person Apple Pay

Me and my brother both have Apple Pay cash card and we both have it set up and everything is functioning normal but when I try to send him money over iMessage or he tries to send me money over iMessage it says the user cannot receive payments from Apple Pay cash but that doesn’t make sense because it works for both of us for anyone else except for each other and it’s very frustrating because the main reason why we set it up is so we can transfer money to each other please help.