Plan not found or checkout is not available
Premium/coupon flows show premium.planNotFound when the selected plan cannot be purchased.
Why this happens
Stale plan selection, unpublished plan, or coupon apply against a plan that is not checkout-eligible. Sibling of the longer “…for this group” API error.
Diagnose and fix
1. Return to pricing; pick the plan again.
2. Admin: ensure the plan is published and has a valid price.
3. If a coupon was applied, clear it and retry, or fix coupon plan restrictions.
4. See Plan & pricing and Buy Premium / Premium Pro.