Endpoints for custom modules in API V8

I’m trying to use API V8 to get and post records in custom modules but none of the endpoints I’ve tried seem to be working and are giving me errors.
so far I’ve tried:
Api/V8/module/custom (400)
Api/V8/custom/module (404)
custom/Api/V8/module (404. didn’t think this one would work but I thought I’d try)

Not sure what the proper endpoint would be so any help would be appreciated.

P.S.
I can get and post to regular modules just fine it’s just custom modules that seem to be not working

EDIT:
I did initially try without custom and it didn’t work but I found out my issue was that I wasn’t including my custom package key.
ie Api/V8/module/KEY_Module