[FIX] STC 5G Hotspot on S24 Ultra – Apps like EZVIZ not working (Ping fails too)? Here’s the solution.

Spent a good chunk of time diagnosing why my EZVIZ HD cameras (and ping) wouldn't work through my S24 Ultra's 5G hotspot on STC, while other apps like YouTube and Chrome were fine. Hopefully, this saves someone else the headache.

Symptom:

• Samsung S24 Ultra, STC SIM, 5G hotspot enabled.
• Connected device gets internet, but specific apps (EZVIZ, some banking apps, some games) fail to connect.
• Ping tests from the connected device to 8.8.8.8 fail completely or time out.

Root Cause:
The default STC APN for 5G on the S24 Ultra was set to APN Protocol: IPv6. The phone was assigning an IPv6 address to tethered clients, but the routing/IPv6-to-IPv4 translation (NAT64) appears to be broken or not supported for these specific applications. EZVIZ, in particular, doesn't handle a pure IPv6 tethering environment gracefully.

The Fix:
Change the APN protocol to dual-stack so the phone can use IPv4 when IPv6 fails.

Steps:

1. On your S24 Ultra, go to Settings.
2. Tap Connections.
3. Tap Mobile Networks.
4. Tap Access Point Names.
5. Tap the STC APN that is currently active (blue dot).
6. Scroll down to APN protocol.
7. It's probably set to IPv6. Change it to IPv4/IPv6.
8. Tap Save (three dots menu, top right).
9. Toggle Airplane Mode on and off.
10. Re-enable your mobile hotspot and connect your device.

Immediately after this, my ping tests succeeded, and EZVIZ connected without any issues.

If This Doesn't Fix It:
Also, check Private DNS (Settings > Connections > More Connection Settings). Turn it Off if it's set to Automatic or a custom provider. On STC's 5G, having both IPv6 issues and Private DNS interference can break P2P apps.

TL;DR: STC's 5G APN defaults to IPv6-only on the S24 Ultra, breaking apps that can't handle it. Changing APN protocol to IPv4/IPv6 fixes it instantly.

Hope this helps someone. Post your results if it worked for you or if you found another carrier-specific quirk.