How to monetize a discord server with 13k people

Hey,
A friend of mine got a really active community on discord with 13k users and we want to monetize it. He already makes 100$/m with donation.

The typical user of his server is a 18/25yo nerd guy 😊

I already have the idea to build a merch and doing some affiliation with cd keys store or something like this

Do you have another idea ?