When you save a coupon that is currently attached to one or more active subscriptions, Sprwt opens the Recurring Discount – Apply to which subscriptions? modal so you decide who is affected:

• New subscriptions only (default) — active subscriptions keep their current rate; only future sign-ups get the new terms.
• New subscriptions + re-apply to active on renewal — if the recurring toggle is on, every active subscription with this coupon is recalculated from its original price with the new value/type and billed at the new rate from its next renewal.
• If you saved with the recurring toggle off, the second option reads New subscriptions + remove from active on renewal: the affected subscriptions return to their full rate and the coupon is detached from them.

The hint line tells you how many active subscriptions are involved. Click Save Changes to confirm or Cancel to go back.