This is a bug with the input box that was fixed in v1.33.0, when you try to edit the port it removes the /ofs path and you can’t add it back.
You can open MultiFunPlayer.config.json in a text editor while MFP is not running, search for "OFS", and under "Uri" field enter the correct url. The default is "ws://127.0.0.1:8080/ofs".
This will fix the issue as long as you don’t try to edit the Endpoint in UI.