[Twisted-Python] txsni + alpn + acme (letsencrypt)

Hello. Can you help me to learn to debug tls problems in twisted? I was disappointed that txacme, an automatic way to get certificates for twisted web, stopped working, so I'm trying to add a responder for the new challenge type. It sends a special certificate if the CA negotiates acme using alpn, proving domain control, then you get a certificate. Seems to work with openssl s_client but letsencrypt says "no application protocol". Anyone know where that error comes from? https://github.com/glyph/txsni/pull/26