HELP , Telemtetry will not connect " no heartbeat received"

so I got them to read each other finally but when I go to connect them together, it still says no heartbeats received , you know why that may be ? or what I can possibly do next ?

I have version 1.3.74 of mission planner and I’m using ardurover on pixhawk 2.4.8
and I’m using the v2 915 MHz telemetry radio

can someone please help, I’m on a deadline ,
thank you!IMG_7527