My friend invited me to Qingdao to eat seafood. How to reply?

First of all, thank you for coming. It can be said that my old friend's kind invitation made me disrespectful. You can also say that, ok, let's have dinner together. Your treat, I'll pay the bill, and you decide the location. Or, thank you for your invitation, but I really have already eaten. Next time, next time it's my treat.

Invitation means inviting people to their own places or appointed places.