stop port 3000 mac

sudo lsof -i :3000
kill -9 PID

sudo lsof -i tcp:3000 

sudo lsof -i :3000

lsof -n -i TCP:8080
COMMAND   PID   USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
node     54762   user   23u  IPv4 XXXXXXXXX      0t0  TCP 127.0.0.1:http-alt (LISTEN)
PID // is second field in the response . Then, kill that process:

kill -9 54762 // here put PID number found on the table 54762