This is even not the correct board to discuss if you are selling a coupon code but you can still sell your coupon code here in the forum. Since we all know that there are scammers then best choice to receive the payment is by using escrow to make it safe to both the buyer and the seller.
I certainly agree with you. It isn't the right thread for you to sell so you better find the accurate place for you to sell your Coupon code. I'm sure that someone would buy it but you have to be mindful, scammers might grab this chance so you better find a legit way to transact.