Recreating flask api call in Android with Retrofit
Well it seems it took the addition of a bounty to force me to work this out :(
This is simply my missunderstanding of basic curl. Obviously the curl request was putting the data in the body whereas I took this for another header. Simply changing the code on server to look for request.header or changing the id to be in the @data part of a retrofit request worked.
can't believe I have wasted so much time and bounty on this blindly obvious error.