Unfortunately, we have little visibility over the reason for payments being declined. You can try using the same card after a while, or try another card.
If an automatic payment attempt (to renew your monthly/annual plan) fails, we'll send an invoice to the registered billing email ID. Unpaid invoices will also be visible on the billing page
Payment instructions can be found in the invoice itself.
Contact us at sales@getpostman.com for more information.