A user reports on #wikimedia that they are unable to login on Phabricator with their Wikimedia account (successfully logged in at least on meta.wikimedia.org); an errror <mwoauthdatastore-callback-not-found> is shown.
The desktop site was used, through the default browser of a Samsung/Android tablet.
Phabricator search fails me but other search engines brought me to the perhaps tangentially related T74654.