SIM related issues may include one or several of the phenomena listed below:
Cannot read SIM card
1. Remove the SIM card to check if SIM card has any damages or is wrongly inserted.
2. Cross-check if the same SIM card can be used in other devices or try a different SIM card.
3. Open "Setting"->"SIM & Network setting" -"SIM Settings" to check whether one of the cards is deactivated. If yes, please activate it.
4. Change to another SIM card.
If this issue only occurs when using a single SIM card, contact the network operator for a SIM replacement.
If the issue persists even after trying more than two different SIM cards, please contact OnePlus for after-sales support.