Hot configure the newtork between gstreamer and Kinesis Video Stream?

I've been trying (on and off - mostly off as I keep having problem after problem) since last year, to get a video conferencing running on an EC2 instance which can only connect to an RTMP server to push media to Kinesis Video Stream using gstreamer running on an EC2 instance:
After many problem building the gstreamer
https://forums.aws.amazon.com/thread.jspa?messageID=857559ᗗ
and getting an intermediate RTMP-RTSP converter:
https://forums.aws.amazon.com/thread.jspa?messageID=857331ᓳ

I start to get things working but still face issue. Here is were I am:

1. The video conference servers connect using RTMP to a crtmpserver on an EC2 instance
2. At this stage, I can connect using VLC and see the video by opening temporarily the RTSP port on the Group Policy of the crtmpserver and gstreamer EC2 instance - so that part works
3. Start gstreamer on that same EC2 instance and get it to connect using RTSP to the localhost crtmpserver and passing my kinesis stream name in parameter.

The problem is that I do see media coming in gstreamer but on the Kinesis side, I do not see anything coming in.

I try to find some information about how the traffic flows from gstreamer to Kinesis but couldn't find any information:
what is gstreamer connecting to ? how? on which port?
I had the idea to create an endpoint in my VPC for Kinesis Video Streams and open all traffic between the two ENIs but there's no such Endpoint (only Kinese Streams)...

Any advice on the networking between gstreamer and Kinesis ?

Thank you in advance,
Matthieu