I see that Larix Broacaster supports both RTSP and RTMP.
https://wmspanel.com/larix_broadcaster
RTMP is more robust as it doesn’t use UDP packets which can result in packet loss. In addition you may not have UDP ports 6970-9999 open for data transport when using RTSP. This would provide a connection but the actual data would not be coming through. This may explain why you are seeing an encoder connection but nothing is coming out.
Run WireShark or TCP dump on your server to see if video packets are heading in. You can filter RTSP per the WireShark instructions below.
https://wiki.wireshark.org/RTSP
You will need to turn off RTMP Source Authentication because Larix Broadcaster does not want to infringe on any of Adobe’s patents.
http://blog.wmspanel.com/2017/06/faq-larix-mobile-broadcasting-sdk.html
For testing purposes, please switch from RTSP to RTMP, and let us know how things work out for you.