There's a much easier way. MonaServer works pretty well in the little testing that I've done. You can either build it yourself using their GitHub stuff, or you can just use their prepackaged 32bit version which is what I've tested with for the time being, and seems to work really well.
When ya unzip the file, you need to go into the www folder, then into the live folder, and create yet another folder called "xyz" (not sure if that's required, but its what I read and it seems to work).
After that, you just run the program. It'll make a RTMP server on your computer, and it'll have a cmd prompt like window appear reading out all the events that are going on.
Now, you open up the GoPro app on your phone, turn on the GoPro, connect to the GoPro, and set it to live stream via RTMP (I think its listed as 'other service' or something).
You connect it to your WiFi (assuming your computer is connected to the same network as well, either by Ethernet or WiFi), put in:
"rtmp://<YOUR COMPUTER'S IP ADDRESS>/live" without the quotes. Submit the settings, tell it to "Go Live" and you should see the cmd prompt window fill with text about a new source/stream being found.
Now! in StreamLabs OBS, you create a new "Media Source" named whatever you want. Inside its properties, you need to UNCHECK "Local File".
In the "Input" field, all I had to do was type "rtmp://" without the quotes, and it immediately found the stream from the RTMP Server/GoPro. You may have to fully type out the "rtmp://<YOUR IP ADDRESS>/live" (without quotes) if it doesn't load for you, but again, I didn't have to, so I didn't try it. I just had ta type rtmp:// and again, it immediately found the stream and started displaying it.
HUGE NOTE!!!!!
There is nearly a 3 second delay between what the GoPro sees and what you see inside StreamLabs OBS. This seems to be on account of the prepackaged version having a 3000ms (3 seconds) buffer set by default. I have yet to find any way what so ever to change this, so I feel this MIGHT be something you can only config during the initial 'building' of the application from its source...
Quick Edit:
I remembered this was about OBS, so I'll include the stuff that I can remember about OBS here.
You should be able to do the exact same thing mentioned above with the generic "Media Source". But I believe OBS has an actual RTMP source if I'm not mistaken. Its been a long time since I'm used OBS itself... And figured that since this thread had alot to do with my own issues trying to get my GoPro Hero 8 to connect to a stream, I'd post what I had found while browsing the interwebs here. I hope this helps anyone who stumbles across it!
github.com
www.helmutsteiner.com
community.gopro.com
