Hoping this is on-topic. If not I can delete.
I own a couple of FOSS projects on Github, and have been toying with the idea of adding some kind of bounty to a few issues, since I do get a (small) amount of income via Patreon from which I’m happy to use to encourage contributions.
I’d rather keep things visible inside Github itself rather than hosting issues on yet another third-party site I would need to administer. I know there have been services like this in the past, but they seem to eventually stop paying out bounties and just disappear.
I’ve seen “boss.dev” showing up in my Google results and it looks to do what I want, but I’m skeptical since there seems to be no reviews or community around that tool.
There is rysolv which is under the AGPL but it probably needs some work (see this and this issues).
On the closed source side there is algora and replit.