Use linux commands “lsof” or “ss” with options to identify the process which already uses port 9002, then decide how to proceed (e.g. kill that process, or some other resolution more appropriate for your network and users).
For instance, like this (scroll this discuss window to the right to see processes):
$ ss -tulpan 130 ⨯
Netid State Recv-Q Send-Q Local Address:Port Peer Address:Port Process
udp UNCONN 0 0 192.168.0.103:3702 0.0.0.0:* users:(("python3",pid=38668,fd=30))
udp UNCONN 0 0 239.255.255.250:3702 0.0.0.0:* users:(("python3",pid=38668,fd=28))
udp UNCONN 0 0 10.0.3.1:3702 0.0.0.0:* users:(("python3",pid=38668,fd=12))
[...]
tcp ESTAB 0 0 192.168.0.103:45164 64.227.130.54:443 users:(("firefox-esr",pid=24872,fd=28))
tcp ESTAB 0 0 192.168.0.103:35680 34.107.243.93:443 users:(("firefox-esr",pid=24872,fd=30))
tcp LISTEN 0 32 [fc11:4514:1919:810::1]:53 [::]:*
tcp LISTEN 0 4096 [::1]:631 [::]:*
tcp LISTEN 0 511 [::1]:6379 [::]:*
tcp LISTEN 0 200 [::1]:5436 [::]:*
tcp LISTEN 0 244 [::1]:5432 [::]:*
tcp LISTEN 0 244 [::1]:5433 [::]:*
tcp LISTEN 0 244 [::1]:5434 [::]:*
tcp LISTEN 0 200 [::1]:5435 [::]:*