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 you see this error while purchasing the annual plan, you can pay via ACH / wire-transfer / check. Contact us at firstname.lastname@example.org for more information.
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 - https://app.getpostman.com/pay/billing. This invoice can be paid via ACH / wire-transfer / check - further details can be found in the invoice itself.