1. Reason:1.It may be that your earbuds charging pins are not in good contact with the pin of the charging case or the charging pin is dirty, resulting in poor charging contact. 

                  2.Or Maybe it's because your charging case has no electricity.
 2.Solution:1.First, you can check whether the Airwings of the earbud blocks the charging pin,then put the earbuds back into the charging case and toggle it to ensure proper contact; 

                   2.Clean the charging pin with an alcohol wipe; 

                   3. then put the earbuds into the charging case and charge the case and earbuds with the charging cable at least for 10 minutes.