So I successfully set it up on a different wifi network once, but then when I tried to use it somewhere else it stopped working. I knew I need to change the wifi setup, which I did too. I kinda wanted to get it down quickly so I thought I will just reformat it and then try to redo every step again, but then I couldn't make it work again.

When I started the service at the last step with shairport-sync -d , I couldn't see it on my iPhone. So first I checked if the daemon is running with ps | grep shair which showed it runs:

1887 root      4360 S    /usr/bin/shairport-sync -c /var/etc/shairport-sync-shairport_sync.conf                                                          
2029 root      1216 S    grep shair

Then I checked the following too: shairport-sync -v

alsa output device name is "default".
Version: "3.1.6-mbedTLS-tinysvcmdns-ALSA-metadata-sysconfdir:/etc"
statistics_requester status is 0.
daemon status is 0.
deamon pid file is "/var/run/shairport-sync/shairport-sync.pid".
rtsp listening port is 5000.
udp base port is 6001.
udp port range is 100.
player name is "Omega-AB33".
backend is "(null)".
on-start action is "(null)".
on-stop action is "(null)".
wait-cmd status is 0.
on-start returns output is 0.
mdns backend "(null)".
stuffing option is "0" (0-basic, 1-soxr).
resync time is 0.050000 seconds.
allow a session to be interrupted: 0.
busy timeout time is 120.
drift tolerance is 0.001995 seconds.
password is "(null)".
ignore_volume_control is 0.
volume_max_db is not set
playback_mode is 0 (0-stereo, 1-mono, 1-reverse_stereo, 2-both_left, 3-both_right).
disable_synchronization is 0.
use_mmap_if_available is 1.
output_rate is 44100.
output_format is 3 (0-unknown, 1-S8, 2-U8, 3-S16, 4-S24, 5-S24_3LE, 6-S24_3BE, 7-S32).                                                                    
audio backend desired buffer length is 0.150000 seconds.                                                                                                  
audio backend latency offset is 0.000000 seconds.                                                                                                         
audio backend silence lead-in time is -1.000000 seconds. A value -1.0 means use the default.                                                              
volume range in dB (zero means use the range specified by the mixer): 0.                                                                                  
zeroconf regtype is "_raop._tcp".                                                                                                                         
decoders_supported field is 1.                                                                                                                            
use_apple_decoder is 0.                                                                                                                                   
alsa_use_playback_switch_for_mute is 0.                                                                                                                   
no special mdns service interface was requested.                                                                                                          
configuration file name "/etc/shairport-sync.conf" resolves to "/etc/shairport-sync.conf".                                                                
metadata enabled is 0.                                                                                                                                    
metadata pipename is "(null)".                                                                                                                            
metadata socket address is "(null)" port 0.                                                                                                               
metadata socket packet size is "500".                                                                                                                     
get-coverart is 0.                                                                                                                                        
loudness is 0.                                                                                                                                            
loudness reference level is -20.000000                                                                                                                    
Successful Startup                                                                                                                                        
Unable to listen on IPv4 port 5000. The error is: "Address in use".                                                                                       
Unable to listen on IPv6 port 5000. The error is: "Address in use".                                                                                       
fatal error: Could not establish a service on port 5000 -- program terminating. Is another instance of Shairport Sync running on this device?             
Request to shut down all rtsp conversation threads                                                                                                        
asking playing threads to stop

So I could see there was some issues and couldn't start properly and has to do with port 5000. Then I wanted to check if something else maybe running on port 5000, so I did: netstat -nlp, which resulted the following:

Active Internet connections (only servers)                                                                                                                
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name                                                          
tcp        0      0 0.0.0.0:5000            0.0.0.0:*               LISTEN      1887/shairport-sync                                                       
tcp        0      0 0.0.0.0:4200            0.0.0.0:*               LISTEN      1777/shellinaboxd                                                         
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      1294/uhttpd                                                               
tcp        0      0 192.168.100.128:53      0.0.0.0:*               LISTEN      1836/dnsmasq                                                              
tcp        0      0 127.0.0.1:53            0.0.0.0:*               LISTEN      1836/dnsmasq                                                              
tcp        0      0 192.168.3.1:53          0.0.0.0:*               LISTEN      1836/dnsmasq                                                              
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      1258/dropbear                                                             
tcp        0      0 0.0.0.0:1883            0.0.0.0:*               LISTEN      1589/mosquitto                                                            
tcp        0      0 :::5000                 :::*                    LISTEN      1887/shairport-sync                                                       
tcp        0      0 :::9001                 :::*                    LISTEN      1589/mosquitto                                                            
tcp        0      0 :::80                   :::*                    LISTEN      1294/uhttpd                                                               
tcp        0      0 ::1:53                  :::*                    LISTEN      1836/dnsmasq                                                              
tcp        0      0 fe80::42a3:6bff:fec0:ab35:53 :::*                    LISTEN      1836/dnsmasq                                                         
tcp        0      0 fe80::42a3:6bff:fec0:ab33:53 :::*                    LISTEN      1836/dnsmasq                                                         
tcp        0      0 fd1d:48c4:7633::1:53    :::*                    LISTEN      1836/dnsmasq                                                              
tcp        0      0 fe80::42a3:6bff:fec0:ab33:53 :::*                    LISTEN      1836/dnsmasq                                                         
tcp        0      0 fe80::42a3:6bff:fec0:ab34:53 :::*                    LISTEN      1836/dnsmasq                                                         
tcp        0      0 :::22                   :::*                    LISTEN      1258/dropbear                                                             
udp        0      0 192.168.100.128:53      0.0.0.0:*                           1836/dnsmasq                                                              
udp        0      0 127.0.0.1:53            0.0.0.0:*                           1836/dnsmasq                                                              
udp        0      0 192.168.3.1:53          0.0.0.0:*                           1836/dnsmasq                                                              
udp        0      0 0.0.0.0:67              0.0.0.0:*                           1836/dnsmasq                                                              
udp        0      0 0.0.0.0:5353            0.0.0.0:*                           1887/shairport-sync                                                       
udp        0      0 0.0.0.0:5353            0.0.0.0:*                           1443/avahi-daemon:                                                        
udp        0      0 :::547                  :::*                                1194/odhcpd                                                               
udp        0      0 ::1:53                  :::*                                1836/dnsmasq                                                              
udp        0      0 fe80::42a3:6bff:fec0:ab35:53 :::*                                1836/dnsmasq                                                         
udp        0      0 fe80::42a3:6bff:fec0:ab33:53 :::*                                1836/dnsmasq                                                         
udp        0      0 fd1d:48c4:7633::1:53    :::*                                1836/dnsmasq                                                              
udp        0      0 fe80::42a3:6bff:fec0:ab33:53 :::*                                1836/dnsmasq                                                         
udp        0      0 fe80::42a3:6bff:fec0:ab34:53 :::*                                1836/dnsmasq                                                         
udp        0      0 :::5353                 :::*                                1443/avahi-daemon:                                                        
raw        0      0 ::%1:58                 ::%4460556:*            58          1194/odhcpd                                                               
raw        0      0 ::%1:58                 ::%4460556:*            58          1194/odhcpd     

I really don't know what is going on and why is it not deploying properly.

I am using an Omega2 with an Expansion Dock.

I also edited the config file at /etc/config/shairport-sync like :

# Use OpenWrt UCI config
config shairport-sync 'shairport_sync'
        option enabled '1'
        option respawn '1'
        ...
        option name 'Shairport-Sync-%v-%h'
        option password ''
        ...
        option mdns_backend 'tinysvcmdns' # avahi/external-avahi/dns-sd/external-dns-sd/tinysvcmdns

Does anyone have some ideas or suggestions how can I resolve the issue with port 5000? I tried to google it, but nothing useful came up.