Try this solution
Make sure the button is physically pressed, a tap will not be enough. Check the image below that you are using the correct command for your desired action.
Ensure the controls have not been disabled in the app
Controls can be disabled to suit the way you use your earphones in the settings of the Melomania App. If any of these are turned off, they will not work until they are turned back on.
Perform a factory reset of your earbuds
1 Place both headphones in the charging case.
2 Press and hold both buttons until the earphone LED's flash white.
3 Wait for the LED on each Melomania 1+ to blink blue three times.
4 The LED will then go back to the “breathing” white display.
5 At this point, you can release the buttons as the reset procedure is complete.
6 The earphones will no longer remember any of the devices that have previously paired with them.
7 When removing either 'Melomania 1+ L' or 'Melomania 1+ R' after a reset, you will hear the voice prompt saying “Waiting to Pair”.