When I try to reinstall macOS a pop up appears saying the recovery server could not be contacted , what does this mean?

Is the computer being booted into Recovery Mode Command +r ? When booting this way - one must have an Active and Functioning Internal Connection.

For best results - connective Ethernet Cable to Router. If via Wifi - immediately at entering Recovery Mode - look for Wifi Icon and you must click it to Manually Input the Wifi Password to establish an Internet Connection.