When GrinPro.io miner starts mining it also starts listening on http://0.0.0.0:5777
The port can be changed by argument "api-port" at startup e.g. ./GrinProMiner api-port=6666
Four zeroes in the listening IP address means, that it can be accessed also from other computers on the network, not just localhost.
So it may look something like http://192.168.1.113:5777 depending on your IP address.
The root URL returns simple HTML dasboard with basic info about the miner.