One Nugget Short Of A Combo

I go to pick up some food on my way to work. I have a coupon for a free order of nuggets and I show the cashier. She puts in two orders of nuggets.

Me: “Excuse me, I only ordered one.”

Cashier: “Yeah, but you have to get two to use the coupon.”

Me: “No, it’s a free nugget with any purchase. I’m also getting [item].”

Cashier: “The system won’t let it work, otherwise. Your total is [amount].”

I don’t want to cause a scene, so I pay. When I get to work, I write a complaint online. I include screenshots of the coupon, where it states nothing about having to buy two orders of nuggets. I get a call later on.

Caller: “Hi, this is [Manager] at [Fast Food Restaurant]. I read that you had an issue with a visit earlier?”

Me: “Yeah, your cashier said I had to buy two orders of nuggets to get one free when the coupon is for one free with any purchase. I checked after I left, and there is no mention of the purchase having to have another order of nuggets. I paid for the second, only because she didn’t seem like she’d want to back down.”

Manager: “Let me look… Okay, is it the coupon on the [Company] app?”

Me: “Yes.”

Manager: “Okay, it does clearly say, ‘Any purchase.’ I don’t know why she’d think it had to be another order of nuggets. If you still have your receipt, I can refund you for your order. I could also offer a couple of coupons for free meals.”

Me: “I’ll take the coupons. I can pick them up after work today.”

I’ve only seen that cashier making food now, not at the register.