To solve the issue, try the following solutions:
1. Turn your phone's Bluetooth off and on, or restart your device to try and establish a connection.
2. If the problem persists, place both earbuds in the charging case, close the lid and wait for 30 seconds to allow the earbuds to reboot. Alternatively, place them in the case and open the lid and long-press the function key for at least 10 seconds to restore to factory settings. Then try connecting again.