No rtmp always runs on 1935 and there is no fall back on 80...However you can configure rtmp to run on any port other than 1935, which however is not recommended. If 80 is the only port then instead of rtmp you can try using rtmpt(i.e rtmp tunneled over http) which runs on 80, since underlying http runs on 80. I am pretty confident that the issue is your network setup and ports/IPs being blocked.IMHO, It has nothing to do with AMS setup.
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