you have to open ports 7171 and 7172 on ur routers site if u use a router if not idk
Yea he has to open port 7171 & 7172. But i also had a problem i opend all ports inkl. 7172 and still pepole couldn't connect and i changed to 7272 then it work'd so i suggest try first to open 7172 and if it does'nt work open a port 7272 and open serverfolder/config.lua
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Edit:
gameProtocolPort = 7172
To:
gameProtocolPort = 7272