I dont know if there are any adult content restrictions on these, but bountysource, opencollective, and issuehunt may be good options.
BountySource, for example, can do bounties and salts. Salts are recurring donations, and a bounty would be for a specific feature (new server, custom patches, patches to upstream, etc).
Might be a viable option so thought I’d mention.
That's a wild take for 'Message an admin when there is a problem with a mod, here are ways you can reach us'.