When processing an order, you might run into the "Insufficient account balance. Account exception Exception with code XXXXXX; module XX, category X, item X" error.
This error is shown when the account through which you are trying to process the orders has insufficient funds.
To solve this issue contact your USPS provider to get instructions on how to add funds to the account, or add funds if you already know how to do it.
After doing so, reprocess the order.