I use RunnerUp from F-Droid and it works great:

https://f-droid.org/packages/org.runnerup.free/

I don’t think mutual aid can work well like that on the internet. Works great in person, works OK for GoFundMe-type stuff like “I had something happen to me that will take a lot of money to fix”. Too easy to scam and grift for small stuff like this though, where for all you know they’re just a very clever dog on the internet.