Multi OBS Controller plugin communicates with OBS Studio via OBS Websockets.
Follow these steps to configure the Websockets Server for each instance of OBS Studio:
1. Open OBS Studio and go to Tools > Websocket Server Settings
2. Check "Enable Websocket Server"
3. Configure the Server Port and Server Password
4. Apply and close the settings window
Once the Websocket Servers are configured, add here their settings: