All transactions go through your Printful Wallet that's created once you sign up with Printful. This helps to ensure quicker payment processing and fewer transaction errors.
Each time an order goes through, your credit card or Paypal will be billed and money will be deposited in your Printful Wallet. Then we withdraw the cost of fulfillment from your Wallet.
When you look at your payment history, you'll see the amount that's deposited to your Printful Wallet from your billing method, and you'll see the amount that we withdraw for fulfillment.
You can also manually add funds directly into your Printful Wallet. Then when a new order comes in, the cost for fulfillment will be withdrawn directly from here.
To add money to your Printful Wallet, go to Billing → Printful Wallet, and click “add money.” Then choose the amount you would like to deposit either by credit card or Paypal. Note that if your Printful Wallet is empty and you haven't set a primary billing method, your orders will show up as “failed” and won't go through until you've manually approved and paid for them.
You can find more info on setting a primary billing method here.