Where are you stuck
I'm sending a multipart http message (json + pcm audio) to the Alexa endpoint, but they reset the connection and I have no idea why. When I interrupt my data sending by returning NGHTTP2_ERR_DEFERRED from my data_source_read_callback() to give nghttp2 time to read from the socket to maybe retrieve some error message that would help me, I only get a settings frame and after that its "mbedtls_ssl_write returned -0x50", which means the peer reset the connection.
It works in my Java prototype. Its totally infuriating.