Hello DaisyMeathead.
Thank you for using Apple Support Communities. It sounds like you were attempting to add a card to the Wallet app but not sure if it's ready to be used. Allow us to share some information with you. If you're able to view your card within the Wallet app, tap on the card then tap on the more option on the top right corner of the screen "..". This will display your card details, if your bank or card issuer requires information, it should be posted there. Check out the link below:
Set up Apple Pay - Apple Support
Review the section under "Add a card on your iPhone", it will mention security codes. You should be OK to use it if nothing is listed within your card details. If an issue arises, you can always remove and re-add the card again to make sure everything was properly set up.
We hope this information is useful. Best of luck.