Web filters work at the network level. They work by acting as the Domain Name System, or DNS for short. This system is responsible for telling your computer what the "internet address" is for the website you want to visit. For example, if you want to go to google.com, DNS is responsible for taking "google.com" and turning it into an internet address, like 142.251.45.78.

Without DNS, your computer can't connect on the internet. By default, the DNS is assigned by the network you're connecting to. However, you can typically override that default with whatever DNS server you want. This is how Truple's filtering works--it assigns a specific DNS server that filters out connections to bad websites.

Sometimes though, the internet service provider (or mobile data provider) will reject our DNS server. We can only guess why--but generally it's because they want you to use their DNS server. They could want it for a handful of reasons, like to force you to use their own DNS which filters connections, or to track your internet activity so they can sell it to advertisers. Whatever the reason, they own the network, so they can do it. And there's not much Truple or anyone else can do to "fix" it. You'd need to ask your internet service provider (ISP) to allow you to use a custom DNS server.

To check what your DNS server is, you can go to dnsleaktest.com and click "Standard Test". This will indicate the DNS server you're currently assigned to use.