@matthew it can be pretty confusing at first 
. Turbo just expects the server to send down nothing but HTML with the proper HTTP header and it will take care of the rest (although I have run into problems with HTTP requests that aren’t made by link clicking / form submissions).
So whatever framework you’re using you want to turn any JSON parsing / handling OFF on the server and the client.
To better understand what a <turbo-stream> is and isn’t I wrote up a post on it: Finally Understanding <turbo-stream>
Hopefully, that helps!