Here are common reasons for payment to be shown as pending:
Funds are unavailable for payment because they are in reserve to ensure you have enough money to fulfill any returns, chargebacks, or A-to-z Guarantee claims. This is a normal part of selling on Amazon.
Bank account or credit card information is missing or invalid. Both are required for Amazon to initiate a payment, so ensure both are up-to-date in your account settings.
The account had a negative or zero balance at the time of payment. This could happen because of selling fees or product refunds. We might charge your credit card to cover the selling fees in this situation.
Shipment for an order was not confirmed.
For FBA Onsite, reason “Shipment for an order was not confirmed” is the most common: even when payment is approved, it will show as PENDING in Seller Central. You have to ship the product through Seller Flex in order to change status to PAYMENT APPROVED.
Whenever a shipment is available to be processed, it means that the payment was already approved and the order can be processed.