You get 120 characters, because that is roughly what a phone shows on a lock screen before it cuts the rest off. Treat it as one sentence that has to make sense on its own, with no subject line and no second paragraph coming.
What works
- Say the useful thing first. "Closed Monday for a refit, back Tuesday" beats "A quick update from all of us here".
- Be specific about when. "This Friday" is actionable; "soon" is not.
- Give them a reason to come in, not a reason to feel guilty. Nobody responds well to being told they have not visited.
- Write it the way you would say it across the counter, because that is the voice they signed up to.
What makes people remove the card
- Messaging too often. Once a week is plenty for most businesses, and once a month is fine.
- Messaging with nothing to say. A message that is only a reminder that you exist reads as noise.
- Shouting. Capitals and exclamation marks look worse on a lock screen than anywhere else.
- Anything that reads as an advert from a stranger. They gave you their loyalty, not a mailing list.
Send fewer than you think
Every message asks to interrupt somebody, so the question to ask before each one is whether it is worth a buzz at the moment it lands. A card can only be notified once every 24 hours, which stops the worst of it, but the limit is a backstop rather than a plan. Something useful but not urgent, like new opening hours or a change to the reward, is usually better saved and sent alongside the next thing worth reading.
What not to promise
Do not tell a customer you have sent them something and expect them to have seen it. Wallets decide whether to show a notification and nobody is told the outcome, so treat every message as something they may read later on the card rather than something they were handed.
A customer who wants out simply removes the card from their wallet, and there is nothing on your side to tick. Writing messages worth keeping is the whole of keeping them.