Greetings CA0001,
Thanks for visiting the Apple Support Communities! I understand you're unable to set up Apple Pay on your iPhone as expected.
The following guide provides troubleshooting suggestions for when help is needed with adding cards to Wallet for use with Apple Pay: Get help adding cards to Wallet. Within the guide, you'll see how to verify that you're in a supported country or region for Apple Pay, eligible devices that are able to use Apple Pay, checking the System Status page, and more.
If additional assistance is needed, it would be helpful to know more details on the steps you're taking to set up Apple Pay when you receive the error message.
Kind regards.