I’m not a programmer, so I can’t really do it myself. Is it allowed for me to go to some random dude, pay him 20 bucks to write the code, then have him add it to the GitHub?
(If you’re wondering what the app/feature is, I want to be able to shuffle play on the findroid app like you would be able to on the jellyfin web interface )
Some larger projects have what’s called a feature bounty, like others have mentioned $20 is very low for someone not familiar with the codebase to do it, it might be enough for someone already familiar with it (but I seriously doubt it since it involves at least some refactoring of the UI to add a shuffle button). However if more people want that feature they can each contribute a small amount and eventually it would be a value that would justify someone to learn the codebase.
That being said, like someone else pointed out, it seems the app is going through some rewriting, so I wouldn’t expect any new features (especially those involving UI) anytime soon.
Finally there are two issues mentioning shuffle in the GitHub, https://github.com/jarnedemeulemeester/findroid/issues/334 and https://github.com/jarnedemeulemeester/findroid/issues/547 you might want to create an account there and voice your wanting of that feature too, by either adding a thumbs up or a comment explaining why this is important to you.
Good luck, hope you get your shuffle play!
Edit: forgot to answer your question directly, yes, you can pay someone to contribute to an open source project, nothing wrong about that. But as a general rule it would be cheaper to give money to the people who are already working on the project.