I updated the wiki pages:
https://openwrt.org/docs/guide-user/firewall/upnp/upnp_setup
https://openwrt.org/docs/guide-user/firewall/upnp/miniupnpd
Check the new Troubleshooting section.
I also have a CGNAT and for some reason the STUN didn't worked. When executed the natpmpc command it returned:
initnatpmp() returned 0 (SUCCESS)
using gateway : 192.168.1.1
sendpublicaddressrequest returned 2 (SUCCESS)
readnatpmpresponseorretry returned -7 (FAILED)
readnatpmpresponseorretry() failed : the gateway does not support nat-pmp
errno=111 'Connection refused'
Once I specified the external_ip manually it started to working:
natpmpc -a 9999 9999 tcp
initnatpmp() returned 0 (SUCCESS)
using gateway : 192.168.1.1
sendpublicaddressrequest returned 2 (SUCCESS)
readnatpmpresponseorretry returned 0 (OK)
Public IP address : 188.163.41.4
epoch = 12167
sendnewportmappingrequest returned 12 (SUCCESS)
readnatpmpresponseorretry returned 0 (OK)
Mapped public port 9999 protocol TCP to local port 9999 liftime 3600
epoch = 12167
closenatpmp() returned 0 (SUCCESS)
Maybe this can help to you to debug the issue.
@timur.davletshin it would be great if you can review it and something to improve. If you don't have an access just let me know what to add (Links, issues, commands, etc). See my contacts in bio