Please update the wiki [1] to contain the following important information about barcodes.

> Where do you find the barcode for a digital release?
Often they are hidden. A few examples:
For iTunes you can sometimes find them in the thumbnail URL and then do a check with their API.
Deezer has an unauthenticated API which returns the UPC, alternatively you can still find them in the page source.
Qobuz used have them clearly in the URL.
For Spotify use their API.

[1] https://musicbrainz.org/doc/Barcode