Let me guess: your customer said "add extra steak to that order of fries" in the special instructions, or hand wrote a tip onto the paper when your delivery person showed up at their door.
These things happen. The answer truly depends. Let's help you figure out the appropriate path.
First, you'll want to login to your Admin Panel.
1) Click "Refund/Stripe Account"
2) Clicking "Payment History" will bring you to a list of your credit card transactions. If you were looking to add $2.50 to Order #175120 in this case, you would click
3) The blue "Add Payment" button. You'll see the customer's name, card number, a field to enter the additional charge amount and reason. You'll want to enter a reason for your records later, so you'll know why the charge was made.
4) As you see in the example below many customers save their cards to the system for quick future ordering. If you notice Order #173700 at the bottom, that customer didn't save their card to the system, so we don't have it stored to make an extra charge. In this case, you'll need to click
5) the "Add Payment" button on the left. It will take you to a new page. You'll need to call the customer and get their card information over the phone. (see second image below)
6) If the customer hasn't saved their card in the system, please skip the "Choose Customers" field. That only contains customers who saved their card.
A couple final notes:
-It may simply be easier to ask the customer to pay anything additional in cash.
-ALWAYS get consent to charge extra. The quickest way to lose/upset a customer is to take money from their wallet without their approval.
If you have any further questions, feel free to leave them in the comment section below.