The Melomania 1 earbuds do not have any pass codes associated or embedded in them in order to be able to connect to another device. If you are being prompted to enter one this may be an issue caused by your device using an older Bluetooth codec.
If you have already tried generic pass codes such as 0000, 1234, etc, then we would recommend factory resetting the earbuds, or seeing if you are able to connect to your device by bypassing the application, such as the windows media player for example, that is asking for the pass code.
If you wish to perform a factory reset your Melomania 1, please put both headphones in the case then press and hold both buttons until the earbud status lights briefly turn blue.
At this point, you can release the buttons as the reset procedure is complete and the earbuds will no longer remember any of the devices that have previously paired with them.
You will then need to follow the initial setup procedure from scratch including the manual Bluetooth pairing process, achieved by holding down the earphone buttons for 3 secs to enter pairing mode.