i had a heck of a time geting my rust server to work. i could join with my internal ip address but not the public ip. did you forward your ports on your router? have you tried connecting to the internal ip address of the machine in rust console built into the game by pressing f1 on title screen?
i am also having this same issue has anyone been able to resolve the issue AMP from server connect is my public IP on the dedicated machine but am getting the same message that OP is talking about APPID invalid