Sik Radio not connecting to mavlink, 915mhz

Hi, I recently bought an APM 2.8 (not supported I know) and 3dr 915MHZ V1 radio telemetry. I’ve been trying for days to get my Mission Planner to connect it for telemetry data and it just times out “No Heartbeat Packets Received” is all I am getting. Yes, I flashed the firmware, loaded the right drivers, removed hardware flow cables, and everything else I could. I can connect the telemetry and load settings and everything else, I also checked it using Arduino, and to send some characters, it transmits data and works perfectly fine. Mavlink just doesn’t connect and times out. I flashed v1.9 firmware still no luck. I used older versions of the mission planner yet it doesn’t work. It seems the radio isn’t talking to my board or something idk. I have also seen some people facing similar issues. I hope someone has solved this and can give a likely reason to what’s causing this issue.