The number of coupons that can be set for each plan is fixed and new coupons cannot be added.
Please re-edit existing ones for use.

Bronze Plan

Coupons are only available when the stamp card is full.

Silver Plan

In addition to coupons only when the stamp card is full, only one coupon is available for any given number of stamps.

Gold Plan

Two coupons are available for any given number of stamps, in addition to a coupon only when the stamp card is full.