Thank you for contacting OPPO.
With regards to your inquiry, we understand that your phone is not able to use the 2nd SIM card.
We apologize for the inconveniences caused.Please be informed due to the 2G closure in Singapore, all 2G networks will be rendered unusable. Therefore, your 2nd SIM will not be functioning. In order to continue using the 2nd SIM slot, please update your firmware from our website.