Every system I’ve used and currently use you enter the tip amount, so writing how much you want to tip is actually fine. Though I’ll usually ask for you to write in the total or ask if it’s fine if I do. Technically the cc company cares about that line in case of disputes.
The addition is the hard part though, calculating the tip amount is easy. Can you write in just the tip amount and let them figure it out at the POS?
Every system I’ve used and currently use you enter the tip amount, so writing how much you want to tip is actually fine. Though I’ll usually ask for you to write in the total or ask if it’s fine if I do. Technically the cc company cares about that line in case of disputes.
But the receipt in the OP didnt have any math? They just decided on a total and wrote it down.