You carefully enter the correct APN values, back out of the screen, and when you check again — they're gone, or reset back to a generic default. This is frustrating but has a small number of specific causes.
Make sure you're tapping the menu icon (three dots) → Save after entering values, not just pressing the back button. On many phones, backing out without explicitly saving discards your changes.
Check whether your phone or carrier profile has APN editing locked. Some carrier-branded or carrier-locked phones prevent manual APN edits entirely and silently revert to their preset — this is common on carrier-financed devices.
Try creating a new APN entry instead of editing the existing one. On some Android versions, editing an existing (especially a carrier-preloaded) APN doesn't stick, but adding a brand new one does.
Double-check the MCC and MNC values match your SIM's actual carrier — if they don't match, Android may silently discard the entry as invalid rather than showing an error.
If you're on Android 12 or later, check Settings → Network & Internet → SIMs → [your SIM] → Access Point Names — newer Android versions moved this menu and people sometimes edit an old/unused APN slot by mistake.
As a last resort, factory reset network settings, then re-enter the APN fresh. A corrupted network settings database can cause exactly this symptom.
This usually means the phone is pulling a carrier-provided default profile on every boot and overwriting your manual entry — common on carrier-locked or carrier-financed devices.
Yes — text/calling still works over the carrier network even without a working APN, so you can look up your carrier's values on Wi-Fi or ask someone to search it for you.