Your card payment can be declined for a number of reasons. The Moneybase app will show the reason for decline on the dashboard.
If you are using your card for the first time, you will be required to perform a PIN transaction. This may be completed using Google Pay, Apple Pay and other supported wallets, or else using the physical card itself.
Also make sure that you have enough funds in your account to process the payment.
You should also check your card settings to ensure your card is not frozen (in which case you can unfreeze it), or that you have not disabled the relevant settings for example, Swipe, ATM or Online transactions.