On Friday 2nd December the curbi certificate that makes the curbi Internet Filter for iOS work, expired.
This is something that unfortunately happens from time to time with certificates. The fix for this is to just re-activate curbi on your kid's devices.
If you don't use the curbi Internet Filter for iOS right now, this certificate expiry won't affect you. Still, its a good idea to have everything up to date in case you decide to use the Internet Filter later on.
Just reactivate curbi on your kid's iOS devices. Click on the link below to see the detailed instructions on how to reactivate curbi.