There are several error codes that may occur during testing, which are outlined in your user manual. The most common of them are Er2, Er3 and Er8.  Er2 is the result of a contaminated or used test strip being inserted. Remove the test strip and repeat the test with a new strip. Wait until you see the flashing blood drop icon before you add blood. Er3 is the result of not enough blood sample for the test strip to activate. Remove the strip and repeat the test with a new strip, ensuring there is enough blood to be collected into the strip. Er8 is the result of a bluetooth disconnection between the meter and your mobile device during transmission. Double check your meter is connected as a bluetooth device, the readings will sync once the meter is again paired with your phone.