I am using FFmpeg converter to push the RTSP stream to RTMP endpoint (Wowza).
ffmpeg -i rtsp://127.0.0.1:554/live0 -c copy -f flv rtmp://88.888.888.888:1935/live/test
The command first throws below error and proceeds with the conversion.

I can play the stream from RTMP endpoint, but after a few seconds, FFmpeg stucks and RTMP endpoint stops to stream.
Please Let me know if I am missing anything here.
I am open to use other libraries for pushing RTSP to RTMP endpoint
You can add analyzeduration and probesize options.
If it failed again, you can try increasing the analyzeduration and probesize options to 20M and 40M.
If still failed, please post the total console log output.