The fact you see the SEID number indicates the NFC module is probably OK. The fact you receive the terms and conditions means the communication network is working.
Apple can’t block a card. Once the T&C is agreed to and bank receives data, they do the provisioning and adding of the card. If your iPhone doesn’t receive data in a timely matter, the request times out and you get an error. The other possibility is the banks are flagging the device and not allowing the cards to be added. When I say banks, I’m including the payment networks.
This is the data Apple sends.
>>This includes information about (a) the user’s iTunes and App Store account activity (for example, whether the user has a long history of transactions within iTunes), (b) the user’s device (for example, the phone number, name and model of the user’s device plus any companion Apple device necessary to set up Apple Pay), and (c) the user’s approximate location at the time the user adds their card (if the user has Location Services enabled). Using this information, the card issuer determines whether to approve adding the card to Apple Pay.<<
Is any of the data off your iPhone perhaps failing bank verification?
Are logged into your Apple ID and iTunes account is in good standing?
Is the phone number the same on the iPhone and if different, banks have been notified of changes and adjusted their records?
Is you Watch on the same Apple ID and paired to your iPhone?
Is Location Services enabled for Wallet app and using precise location?
Have you traveled recently? Is your iPhone and Apple ID set for your current location? Is the location the same for the banks? In other words you’re in the US, banks are in the US and your iPhone and Apple ID are set to US?
How high a support level have you gotten with the bank? Are you talking to the entry level support person or is your call being escalated?
Just to rule out hardware, you can call (1-800-MY-APPLE) Apple Support and request remote diagnostics on the hardware.
Have you ever used a VPN on the iPhone?