The VPN is the security issue. You can discuss the use of a VPN with Citibank. Citi seems much more restrictive in the use of a VPN than other banks. However, the banking industry as a whole, is becoming much more restrictive in the use of a VPN on secure devices.
You have several ways to proceed. You can discuss the matter with the bank. From what I know of the banking industry, they won’t budge. But it can’t hurt to ask.
The second is to wait 24 hours for the temporary block to expire. Remove any VPN software and the VPN profile (management files) and reset the network settings. It should allow you to add your card. If it doesn’t, they placed a 31 day block on the card.
If you need specifics on any of the resets let me know.