Here is what Apple says about this part of the provisioning process.
“If a terms and conditions ID is returned by the card issuer or payment network with the Check Card process, Apple downloads and displays the terms and conditions of the card issuer to the user. If the user accepts the issuer’s terms and conditions, Apple sends the ID of the terms that were accepted as well as the CVV to the Link and Provision process.
Additionally, as part of the Link and Provision process, Apple shares information from the device with the card issuer or network. This includes information about:”
- The user’s iTunes and App Store account activity (for example, whether the user has a long history of transactions within iTunes)
- 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)
- 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.”
“As the result of the Link and Provision process, two things occur:
- The device begins to download the Apple Walletpass file representing the credit or debit card.
- The device begins to bind the card to the Secure Element.”
“The pass file contains URLs to download card art, metadata about the card such as contact information, the related issuer’s app, and supported features. It also contains the pass state, which includes information such as whether the personalizing of the Secure Element has completed, whether the card is currently suspended by the card issuer, or whether additional verification is required before the card can make payments with Apple Pay.”
Adding credit or debit cards to Apple Pay - Apple Support
So, the process is you enter card details in the Apple Wallet app. Information is encrypted on device and it generally goes to the Payment Network Operator (Visa, Mastercard, American Express etc.) The security code (3 or 4 digit number commonly referred to as CVV) is not sent. If the account number is valid and expiration date current, you’re sent the Terms & Conditions to agree to.
T&C are returned with security code and additional information contained on your device. Now the banks approval process begins. An assessment is applied to the additional iPhone data. Banks to not reveal how their review process works. Many use a 4 path workflow, green, yellow, orange and red. Green is automatically approved, yellow and orange requires additional verification and red is declined. The reviews are designed to appraise the risk.
Velodcity blocks happen when a cardholder attempts to add a card too many times. Again, banks set their own levels, but 5 failed attempts seem to block any future attempts. How long is the block? Only the bank knows and generally they won’t tell the cardholder. However, the block may be as short as 24 hours or as long as 7 days.
When a card has failed, you really only have two paths forward. One is to work with the bank to get an exception made. The second is wait 30 to 45 days with no provisioning attempts during that time period.
Here are two links to posts you may have already read. The first, the OP worked with his bank and got them to make an exception mad. The second is a little more involved and the person even bought a new iPhone and it was still blocked. She waited the 30+ days and then added the cards.
Apple Wallet Disabled - how to resolve ? - Apple Community
Cannot add cards to Apple Wallet on iPhon… - Apple Community