"Connection Lost Internal Exception: java.io.IOException: An existing connection was forcibly closed by the remote host"

My friend is having difficulties joining my realm, and this is what keeps popping; https://cdn.discordapp.com/attachments/698059419740799046/700855455722897408/image0.jpg I have no idea what is causing the issue, I made the binaries private because that is what some forums mentioned, but it didn't do anything. Note that he is using a jetpack (mobile hotspot).