Support Switching to Lower or Same-Priced Plans (with Discounts)

🔍 Problem Statement
As a subscriber, I experience limitations when attempting to switch from my current plan to either a lower-priced plan or a same-priced plan that includes a discount or promotional offer, which results in reduced flexibility, since users cannot adjust their plans to better match their budget or new offers.

💡 User Story
As a subscriber, I want to switch from my current plan to another plan of equal or lower price (including discounted options) so that I can opt into better pricing or promotional offers without needing to cancel and resubscribe.