VoWiFi isn't working on my Flint 2

Router
1

Hi, VoWiFi isn't working on my Flint 2. I have the 4.8.4 stable version installed via Uboot; I upgraded from the 4.8.4 nightly build.
My iPhone shows VoWiFi correctly when I connect it to other routers or access points, but not with the Flint.

2

Hi, I'm using the latest OP24 firmware (4.8.3). Everything works well and runs smoothly on Ukrainian carriers. Android smartphones

3

Check the essential ports UDP 500, 4500 if they’re blocked or not first.

4

Hi, UDP 500 and 4500 seems not blocked
Connection to 8.8.8.8 port 500 [udp/isakmp] succeeded!
Connection to 8.8.8.8 port 4500 [udp/ipsec-msft] succeeded!

5

Try changing DNS settings.

6

With what? I've tried the ISP's ones and Cloudflare's as well.

7

Depending on carrier, some expect their DNS without any intermediate strata like adguard. Is there any ad blocker enabled on the router?.

8

Every now and then, though, I notice that VoWiFi is active on my smartphone, so I don't think it's a DNS issue; I think it's something to do with the router settings. I just need to figure out what...