SIM Card is not detected on the phone even though it is properly installed in the SIM Tray, Maybe one or both SIMs are not recognized. In some cases that I experienced, the SIM Toolkit app on Android that didn't work was the cause of the SIM Card not being recognized.
Clear Data in SIM Toolkit App Samsung Android Phone
You can follow step by step to fix SIM not found in Samsung Galaxy A, S, and Note phone series.
- Insert the SIM Card and turn on the phone.
- Open the Settings menu.
- Tap the Apps menu and find the SIM Toolkit app.
- Tap Storage → Clear Data.
- Tap Back button and open Permissions.
- Click the three-dot symbol in the upper-right corner of the Permissions screen and tap All Permissions.
- Make sure SIM Toolkit has permissions run at startup, retrieve running apps, disable your screen lock, and prevent phone from sleeping.
- Restart the phone.