How to do tcpdump for APM AAA authentication?

Hi, i need some advice.

I've setup an APM for the OTP authentication with Radius server. From the APM logs, i do received the Access-Reject packet from Radius module.

/Common/DEV:Common:b1d4b3bc: RADIUS module: authentication with 'ACB123' failed: Access-Reject packet from host 127.7.0.3:1812 (3)

But from my counterpart, the Radius team said from their packet trace they don't received any Access-Request packet from F5.

How can i apply tcpdump or anyway to find out which host is replying the Access-Reject packet from Radius? Because APM log above didn't tell the actual IP where i want to prove to the Radius team the Access-Reject packet is coming from their end.

Pls share me the commands, thanks.