How do I limit a discount to one use per customer?

Use a campaign with a discount code — either a public code campaign or a link campaign — and tick Limit to one use per customer under Maximum discount rules. It cannot be done on an Automatic campaign, because Shopify's API offers usage limits on code discounts only. The section does not even appear when a campaign's method is Automatic.

Setting it up

1. Open the campaign and set the method to Discount code, or make it a Link campaign (link campaigns are always code campaigns).
2. Find Maximum discount rules on the same step.
3. Tick Limit to one use per customer.
4. Optionally tick Limit number of times this discount can be used in total and enter a number — this is a store-wide cap across all customers.
5. Save.

Both limits are enforced by Shopify at checkout, not by Hype.

A link campaign is usually the best answer here: the customer never types anything, so you get the auto-applying behavior of an automatic discount together with the per-customer limit.

Make sure Shopify can tell who the customer is

Shopify has to identify the shopper to know they have used the code before. Tighten it with the campaign's Customer eligibility section, which works on both methods:

• Logged-in customers only — "Customers must sign in to use discounts."
• Segments — restrict the campaign to one or more customer segments.
• Customers — restrict it to named customers.

Combining Logged-in customers only with Limit to one use per customer is the strongest control Hype can offer.

If the campaign has to stay automatic

There is no equivalent. What you can do instead:

• Restrict it to a customer segment, so only that group is ever eligible.
• Set an end date on the Active dates section to bound the exposure.
• Use a total usage cap on a code campaign rather than an open-ended automatic one.

Careful when switching an existing campaign

Changing a live campaign between Automatic and Discount code deletes the Shopify discount and creates a new one. Hype warns about this: "If the campaign had restrictions (e.g. one use per customer), those limits will be reset, and customers may be able to use the campaign again." Counts start from zero, so a customer who already redeemed can redeem again.

Related

• Common campaign settings
• Discount codes and their limits
• Public and link campaigns