SHELL

ubuntu kill specific port 3000

sudo kill -9 $(sudo lsof -t -i:9001)

ubuntu kill port

You want to use backtick not regular tick:
sudo kill -9 `sudo lsof -t -i:9001`

If that doesn't work you could also use $() for command interpolation:
sudo kill -9 $(sudo lsof -t -i:9001)

kill port 3000 ubuntu

fuser -n tcp -k 9001 

ubuntu kill running port

Kill specific port