custom ip address on port 80 not listening

[Musta Fa]

nginx/1.11.13


i have 4 server IPs, all registered in network interface
and many domains and apps, also on different ports.

all other ports are ok:
custom_ip1:443, custom_ip1:5000, custom_ip1:81
custom_ip2:443, custom_ip2:5000, custom_ip2:81
custom_ip3:443, custom_ip3:5000, custom_ip3:81

but i can not make it listen on custom_ip:80
port 80 is always 0.0.0.0:80

cd /etc/nginx
grep listen -r *
only "listen custom_ip:80;"

why is that??
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