Plan not found or checkout is not available for this group
Role-plan checkout (and related balance/Authorize.net paths) rejected the plan/group (404).
Why this happens
Plan id removed, not sellable, wrong group, or checkout disabled for that role. Distinct from the shorter Plan not found or checkout is not available (coupon/premium client copy).
Diagnose and fix
1. Admin: confirm the plan exists under Plan & pricing — Premium plans / Premium Pro and is enabled for checkout.
2. Member: reopen premium from the pricing page (do not reuse stale roleId URLs).
3. Check group/role assignment if plans are scoped.
4. See Buy Premium / Premium Pro.