Note: Change only applies to "forever" 100% off coupons - it does not apply to amount-off coupons or coupons that have a specific duration.
Rolling out today: Customers who are installing paid apps from the Marketplace, where an app developer has provided a 100% off coupon to the customer, now no longer needs to provide a credit card to install the app.
Before:
After:
They can simply proceed to the installation settings after agreeing to the terms and conditions.
For more information on coupons see the Stripe docs on discounts.