This article covers
Difference between coupon redemptions and applied numbers
When you check the redemption count of a coupon
And when you check in the Subscription index page
The values may not match. It would be that the redemptions count is more than the number of subscriptions that the coupon applied to.
That is because there are cases in which a Subscription_Change is scheduled to happen at a future date and the coupon must have been applied that would come into effect when that subscription change occurs. So technically, the coupon has been redeemed, but currently, it is not showing in the Subscription.
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