(The full English name of APN is AccessPointName, and the full Chinese name is Access Point. It is a parameter that you need to configure when surfing the Internet through your mobile phone. It determines which access method your mobile phone uses to access the network. Sometimes, when you need to repair the APN, you will find that it cannot be changed. Even the commonly used HIAPN cannot be repaired. This is just because you need to repair some files. See the following tutorial for details.
[Mark Android Tutorial] Solution for Android Mobile Phone Repair APN Not Saving. pdf)