Coupon scam/redemption

While trying to sell SMS text to a restaurant owner,
he asked me how did that worked exactly. So then I said:

"Well, you say in your text just to show their cell phones with the coupons at the counter, and they'll automatically get a rebate this way."

"Yeah, but what if my staff simply declare too many coupons?At least, with paper coupons, I have a paper trail so I can count exactly how many were redeemed"

I couldn't find a proper counter to that problem. I use long codes and I was told it wasn't possible to track/confirm that each recipient received the SMS.

If you have a solution, any help is appreciated.

Restaurant Owner should ask his employees to note down the codes and match it later with the code you provided . Or hire a freelancer to make a bot to do all this .

Yeah, I taught about a more technical solution where a different random string is included with every single text but honestly I would rather avoid coding such a thing myself or hiring a freelancer to do so.

You should be running your promotion for a limited time during hours when normally nobody comes in to eat. So even if their friend sent them the coupon, it doesn't matter. At least that person is in the restaurant eating instead of the owner paying 10 employees to serve 4 people.