Apple Pay stopped working on my iPhone 6S plus

A few weeks ago I tried to make an App purchase using ApplePay on my iPhone 6S plus but it would not complete the purchase and said I must add a payment method. I checked and my multiple credit cards were still there with the correct information. A couple of weeks later I tried it again to make a purchase from an Internet retailer and the same thing happened again, and again all the credit cards were there with the correct information. This morning I tried to make an App purchase but it was a repeat Of the other two times. Two App vendors and a retailer lost sales because I did not have the time or patience to do it all again from another device, plus I wanted the App purchases on my iPhone, not on my iPad.

ApplePay still works on my iPad and on my MacBook Pro. The credit card I have set as the primary card to try first is still used by Apple for Internet streaming purchaseS via Apple TV and monthly iCloud payments so obviously the problem is not my methods of payments. It’s a problem with the iPhone 6S Plus.

Does anyone know what the problem is or gave any suggestions?