A phone number. That is the only required field for a loyalty card to work, and everything else you add to that form costs you sign-ups while usually bringing back nothing.
First name, email address and birthday are optional in Kanz. The birthday is limited to the day and the month: the year of birth is never asked for and never stored. It is of no use for wishing somebody a happy birthday, and it is one of the most sensitive things a form can pick up while nobody stops to ask why.
The rule: every field pays its rent
A field on a sign-up form at the counter has an immediate cost, measurable in lost sign-ups, and a deferred one, which is keeping it, protecting it and having to answer for it.
So ask the question this way round: what do I actually do with this data tomorrow morning?
The phone number identifies the person and lets you reach them: it pays its rent. The first name lets you write a message that does not open with a bare "Hello": it pays its rent too, just about. A full date of birth, a postal address, an occupation, a gender, a number of children: none of that turns into an action in a small local business. These are fields collected because a form offered them.
What a wallet card cannot do
There is a difference in kind between a loyalty card in the phone's wallet and an installed loyalty app.
An app can ask for location, contacts, photos and the camera, and can ask again after an update. A wallet pass cannot. It is not an app: it is a data object in the standard format of the two systems, with no code to run. There is nothing to grant because there is nothing running.
That is why the sentence "we do not track your customers" is worth something here and not elsewhere: it is not a promise that can be withdrawn, it is a property of the format.
Consent is a record, not a tick box
When somebody signs up, Kanz writes a line of consent: what, when, through which channel, and under which version of the legal text in force that day.
That last part is the one everybody forgets and the only one that counts on the day the question gets asked. "The customer agreed" cannot be checked two years later if the terms changed in between. "The customer agreed to version 3, on 14 March, from the sign-up page" is a statement that holds.
Unsubscribing takes a single move
The unsubscribe link is on the back of the card and in every message sent. It is signed, it does not expire, and it does the job immediately: no confirmation page, no "are you sure", no exit survey, no account to track down.
That it never expires is deliberate. A card added today still has to be able to unsubscribe in two years, including for somebody who has changed phone in the meantime and has no way left of finding anything.
And the link does one thing only: what it exists for is part of what is signed, so an unsubscribe link cannot be replayed as a card download link, or the other way round. It stays usable as many times as you like, and it can never do anything other than what it was issued for.
A page that tries to catch somebody at that moment is exactly why people end up wary of loyalty programmes in general. The unsubscribe has already happened before the page loads.
The business owner cannot undo it
This is the part that surprises people, and the part to remember.
Once a customer has unsubscribed, no setting on the business side puts them back on the list. There is no path in the product to reverse an unsubscribe, not for the owner of the business, and not for the people who operate Kanz either.
The only thing that can bring them back is the customer, by signing up again through the same public form as the first time. Signing up again is the same move as signing up: nobody is ever made to ask twice.
In the check that runs before every send, the unsubscribe is verified in second position, before the time of day, before the caps, before the budget and before the credits. It is not at the bottom of the list with the rare cases.
What this changes at the counter
A one-field form gets filled in standing up, with a queue behind. A six-field form gets filled in at home, which is to say never.
So ask for the number. Ask for the first name if you intend to use it. And leave the birthday to the person who wants to give it, because that is the person who really is expecting something that day.
The sign-up flow is set out in full here, and the sending rules in another article.