A lock screen message is the wallet pass acting as a communication channel: a line on the lock screen that comes from a pass, not an app. Because the wallet is a system app, the pass reaches the lock screen without the program shipping an app or winning a notification permission prompt.
Messages reach the lock screen along a few routes. A field update paired with a change message announces something that just became true, such as a new balance or tier. A campaign message attached to the pass carries an offer or piece of news. And pass relevance surfaces the pass itself at a useful time or place, such as near a store or before an event, without saying anything at all.
The channel's power is precision, and its risk is the same as every channel: overuse. A pass sits next to the member's payment cards, which is valuable real estate to be evicted from, and deleting a pass is one swipe. Programs that treat the lock screen as a broadcast medium train members to do exactly that. Segmented campaigns, triggered automations and a frequency cap are the discipline that keeps the channel welcome.
Wallets, not issuers, control final presentation, so delivery monitoring matters: a platform should show that a message reached wallets, not merely that it was sent.