What is wrong with this flip flop hub? It keeps spinning both ways, no idea how to fix

That’s the freewheel side, turn the wheel around and the other cog should be fixed

There are pawls in freewheel that are either broken or stuck. If stuck, cleaning and lubrication is all needed to fix it. Either way new freewheel is cheaper. Replacement will be tricky.

It’s fucked. Go fixed.
😂

I thought this was irony at first lmfaoo.

Judging by the rust/abuse of that freewheel plus the lack of engagement (aka it spinning around like that both ways), its dead and needs replacing. Either way youd need a specific BMX/4 peg freewheel remover.

Only a few freewheels are designed/worth the hassle of servicing (white industries and Halo f.e.). It can be done but that looks like your generic throwaway versions, companies like Dicta make them for 10gbp but id recommend getting a better one for lomg term

As its not technically a fixed gear but single speed (welcome to the team), you should post general repair advice/support on r/bikewrench.

Warn you now, their banter is terrific in there