Yes, JSON-LD is also a problem!
I personally would just use a library that translates json-ld to rdf and vice versa. But unfortunately I haven’t found an AP platform yet that creates or understands compatible json-ld.
Many developers seem to understand json-ld as json and not as rdf and that is a big problem. In my opinion most of them don’t speak json-ld!
I’m planning to exchange events with mobilizon S2S, so i would like to play around with it soon. it would be good if a mobilizon expert can help me 
just in case someone knows one
Btw. i left the project that was implementing the AP C2S App and i’ve no idea if it will get openSourc e and if, when this will happen.
But i started last week to model the reception of activities with https://www.enterpriseintegrationpatterns.com/, i am curious if i get further. I would now have to start another AP implementation and I can not yet say whether I have the strength to do so.