How do I enable Apple Pay for CDL upload?

Your profile suggests you have an iPhone 7.

iPhone 8 or later is required for a driver’s license in Apple Wallet.

Add your driver's license to Apple Wallet - Apple Support

Disable the VPN and reset your network settings. Lastly do a forced restart and once your iPhone restarts, login and add your license.

Reset your network settings

If you're using iOS or iPadOS 15 or later, tap Settings > General > Transfer or Reset [Device] > Reset > Reset Network Settings.

If you're using iOS or iPadOS 14 or earlier, tap Settings > General > Reset > Reset Network Settings.

This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you've used before.

Please follow this path,

iphone > Settings > General > VPN & Device Management > delete any files/profiles related to the VPN. Once deleted, restart the device, reset network settings and try again to add the license.

Apple Pay has nothing to do with adding items to your Wallet app. Apple Pay is only a payment service.

Do you use a VPN?