Web server address already in use

[MohamedAlwash]

Hello every one.
Today I installed RPi-Monitor on my RPI4 4Gb. But it's not working because I get this error:
Web server not started because of error: Address already in use rpimonitord stopped because respawning too fast.

I have RPI4 4b. Using Raspbian headless.

What I already tried:

1. Change port from 8888 to 8889 I get same error.
2. When I type

lsof -i :8888

it shows nothing. But when I type this command

sudo netstat -tlnp | grep "\:8888"

it shows me this:

tcp 0 0 0.0.0.0:8888 0.0.0.0:* LISTEN 591/perl

3. I changed the daemon.delay to 120, still same problem.
4. Installed and removed rpi-monitor bunch of time, it doesn't help.
   What can I try more? Can you help me plz?

I have installed ufw en fail2ban on my rpi, does that take effect?

[MohamedAlwash]

Never mind, I found out where the problem is. Because UFW is blocking.