Primary and Secondary SIM not showing/working on my iPhone 12

Likely Reasons Your SIMs Aren’t Showing Up

1. Inserted the Wrong Way ‘Round: Even seasoned tech-savvy folks sometimes pop a SIM in upside-down. Eject the tray, match each card’s notched corner to the tray diagram, and reseat them firmly.
2. Damaged or Worn SIM Cards: Bent metal contacts, scratches, or a little corrosion is all it takes for your iPhone to stop recognising a card. Examine each SIM under good light; if the gold surface looks scuffed or pitted, ask your carrier for a replacement.
3. Carrier-Locked iPhone: If the phone is locked to, say, Carrier A, any card from Carrier B will politely refuse to appear in Settings › Cellular. Check your device’s lock status (Settings › General › About › Carrier Lock) and, if necessary, request an unlock.
4. SIM Tray or Internal Hardware Damage: A bent tray or recent drop can misalign the contacts. Inspect the tray for warps; if nothing’s obvious, an Apple technician can test the phone’s reader.

When to Call in Reinforcements

• If either SIM fails in another phone – contact your carrier for a fresh card.
• If a known-good SIM also refuses to appear – book a Genius Bar or authorised repair visit; your SIM reader might need service.
• If you’re still carrier-locked – request an unlock or use the carrier’s online portal. Unlocks usually take a few minutes to 24 hours.

Pro tip for the future: consider adding an eSIM when your carrier supports it. No trays, no orientation issues—just a QR code and you’re connected. (Plus, it’s one less tiny object to lose under the sofa.)

Run through these steps and your SIMs should quit their disappearing act—no top hat or white rabbit required.

• Go to Settings  > Cellular, then make sure you have at least two lines (below SIMs). To add a line, see Set up cellular service.

Use Dual SIM on iPhone - Apple Support (IN)

Try to restart the phone. Are you using physical sim or e-sim? If for physical sim, remove it and then put it back again.