Is it in the wedding on the wedding at the wedding which one is correct? And how about the words concert? Are they the same?

I have two tickets of a concert. The first is a correct sentence, but the second is wrong. Why can't we use the phrase tickets of? If you've decided that you're just going to go to any concert that is occurring on a certain day, you should use the indefinite article (a). We're going to a restaurant tomorrow.

We're going to a restaurant tomorrow.