Access Point Name settings, otherwise known as APN, are the settings your phone needs in order to connect to data servers. With them, you’re able to connect from your carrier to the internet.
Without these settings, your phone cannot obtain the correct IP address or connect to the correct server; meaning no data. Your APN settings should automatically update and connect to your carrier’s servers when you insert your SIM.
If you are experiencing difficulty connecting to the internet or are losing data services, your APN settings may be wrong. If this is the case then you should contact your carrier as you may be at risk of being overcharged. It is important to remember that you should not change your APN settings unless instructed to do so by your carrier as you will need to use the same settings as them.
If you need to change your APN settings, you can find them on your iOS device in SETTINGS > CELLULAR > CELLULAR DATA and then enter the details given to you by your carrier. Updating your iOS will also reset the settings automatically.
If you’ve purchased a SIM for international use then there may be a chance that you will have to input different settings manually if it doesn’t update automatically. These can be found in the SIMs instructions guide.