If you set up Apple Pay or Google Pay, you will need to set up a PIN number to use the card as a "debit" card. You can set your PIN by calling 1-833-904-2761, and selecting option 4.
Make sure you have your 16 digit number easily accessible, as you will need that in order to confirm your card and set your PIN.
You can also select "credit" instead of "debit", and the transactions should process normally.
If you are awaiting your mailed physical card, and are currently using a temporary virtual card...
You may not be able to set up a pin for Apple or Google Pay until your physical card arrives and is activated. If this is the case, you will only be able to use your Fold Card in your mobile wallet at retailers that are able to run it as "credit".