F5 is not working as proxy solution - Need Help

In our scenario we are sending traffic to F5 from host 10.7.3.225 on port 21 on F5 VIP 10.8.10.85. F5 should forward that traffic to backend server 10.8.5.25 on port 7021 but it's forwarding it on port 21. In pool, node and monitor i am using port 7021 but still it's forwarding traffic on port 21.

Virtual server is configured as standard server. Backend and monitor are configured as tcp 7021.

Below is the expected traffic flow which is not working

10.7.3.225:21>>>10.8.10.85:21>>10.8.5.25:7021

Below is the tcpdump as the backend node is listening on port 7021 but as it's not getting traffic on port 7021 it's sending back Reset packet on VIP

just FYI 10.8.5.20 is the self ip. If you see the packet from 10.8.5.20 to 10.8.5.25 it's sending with localport=21

Can you please help waht's wrong in my config and if you have query to understand the flow please let me know. Thank you in advance.