Untrusted certificate

Hi there ebrahim283,

Welcome to Apple Support Communities. Often, a certificate is related to if you use a VPN or have a profile installed on your device. An installed profile is usually if your device is being managed by a school or business. Let's check a few things.

- Do you use any kind of VPN? If so, let's disable it. To check, go to: Settings > VPN, or disable it from the app.

- Do you have any profiles installed? This might be for work or a certain connection? Check that by going to: Settings > General > Profiles

If so, we'll want to remove that or talk to the IT department of the school or business that manages this device (if that's the case).

- Is your date & time set correctly? If not, this can cause issues with connections. To check, go to: Settings > General > Date & Time

We look forward to hearing how it goes.

Take care.

The certificate has expired.

Which becomes a question of which profile or app or VPN loaded it.

Any website associated with the domain is offline, too.

The domain registration is still valid, and was recently renewed, but uses domain masking, so no info that way.

See reply above for more.