OnePlus
Set Up an APN Manually auf OnePlus
An Access Point Name tells your OnePlus how to reach your carrier network for mobile data and MMS. If this entry is missing, wrong, or got wiped during a factory reset, the phone stays connected to the mobile network but cannot exchange any data.
This mostly happens with prepaid SIMs, MVNOs, or SIMs moved from another device, since automatic provisioning does not always trigger a configuration message. Adding the APN manually solves it in most cases.
Add the APN manually
Open Settings ➔ Wi-Fi & network ➔ SIM & network and pick the SIM card you want to configure. Tap Access Point Names, then Add to create a new profile.
Enter the values your carrier provides for name, APN, and MMSC. Open the menu once the fields are filled in and tap Save to apply the profile.
If mobile data is still unavailable afterward, double-check that the new APN is actually selected, since some devices keep an old profile active until you switch to it manually. A restart also helps the modem pick up the new configuration cleanly.