1, you can attend. Xiamen University teachers have no restrictions on this. You can go to every class without paying.

I suggest you get the course schedule of Xiamen University's advertising major, so that you can know the time and place of class. Just remember to sit down early, but you should be mentally prepared, because class is someone else's class, and if you are next to foreigners, you will be marginalized. You must have a strong psychological quality.