Notifications have to be tied to functionality the user actually wants — promotional or advertising content sent as a push notification, without being explicitly opted into, violates this guideline.
Usually caught after user complaints about promotional pushes, or when a review build's notification permission prompt doesn't match what's actually sent afterward.
"Your app sends push notifications that are being used for advertising, promotions, or direct marketing purposes, which is not permitted per guideline 4.5.4."