a) Please ensure if device did not get connect to the previous input device. If yes, then please forgot or remove it from there.

b) Volume level need to check, and Ensure to set the desired volume level from Mobile Phone and ear buds both.

c) If using online APP then check internet connection.

d) If using online APP, please check its compatibility with Mobile Phone and allow permissions from APP Manager in Mobile Phone.

e) Mobile phone can also have issues in this case. check if the device is working well with other mobile phone 

f) RESET the device

1- Remove device name from Bluetooth Interface
2- Take out the earbuds from the charging case.
3- Tap either of the earbuds 5 times to reset.
4- Place both the earbuds inside the charging case and repeat the pairing process.