#cardinality property referenced in template but never set in coupon redemption form

Problem Description

The commerce-coupon-redemption-form.html.twig template references form['#cardinality'] to determine display format (single vs multiple coupons), but this property is never actually set in the form build.

Current behavior: The template condition {% if form['#cardinality'] == 1 %} will never be true because #cardinality is undefined, so the form always displays in multiple coupons format regardless of the max_coupons configuration.