Maybe you're the one who can write a check, but this is a difficult topic...

I do corporate accounting for baroque software and I can write an invoice and pushing people to pay for it is still quite a sales challenge - you need to be able to talk to high enough people and prove the value of what you're offering on top of the software you are already giving for free. It's not different to a standard issue sales exercise, except a little harder. This is not a skill that most open source project maintainers would consider themselves experts at.

Giving advice like that is very dangerous - "only if you did that, you would make money". It's not a given that it would lead to something more than couple hundred dollars.