I’m sorry but the install documentation is everything but clear, so far I had to add things that were not mentioned in the installation to go ahead.
There are a few FQDNs or URLs involved in order to make things work:
jitsi.mydomain.org/http-bind => should be sent do IP_Prosody_server:5280/http-bind
jitsi.mydomain.org/xmpp-websocket => should be sent do IP_Prosody_server:5280/xmpp-websocket
Are there any other domains/urls in the game ?