Credit card

In order to use Reshopper Shipping, your payment card must be linked to your Reshopper account. As with all other payments you make, a payment can be declined for various reasons.

Insufficient funds

Either there is no money in the bank account to which the credit card is linked, or there are reserved amounts that exceed what the bank believes there is cover for.
In this case, you can either choose to deposit more money into the account, or change your cedit card via "You" -> "Settings" -> "Account" and then scroll down to "Credit card".