Why debit card declined after I’ve been verified

OK, Apple and Apple Cash servicer (Green Dot Bank) cannot approve or decline transactions. Approvals and declines can only be made by your debit card bank or the payment network (Visa, Mastercard).

Let’s start by making sure your iPhone is updated to latest iOS and then do a forced restart. Follow the instructions for the forced restart, it’s more than turning on and off.

Update iOS on iPhone - Apple Support

Force restart iPhone - Apple Support

If you’re using a VPN, it must be deleted from the device. Payment Networks typically will block any communication using a VPN.

If that doesn’t work, please reset 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.

Reset network settings would be the final step, then it’s back to the bank, as I suspected

What do you mean declined? Are you trying to transfer funds or make a purchase? Who said your card is declined, your bank, Apple Pay or who exactly?