Allow Multiple Subscription Plans and Intervals Under a Single Product

Instead of having a separate product for each plan, add the ability to include multiple plans under a single product. For example, a SaaS with 3 subscription plans across 2 billing intervals results in 6 variations ($3 \times 2$):Plan 1 – Monthly & YearlyPlan 2 – Monthly & YearlyPlan 3 – Monthly & YearlyAdditionally, users should be able to switch between plans and billing periods directly from the checkout page.