change_plan

What it does

Start or change a plan (starter, growth, pro, business), or cancel with none. With no plan this returns a checkout URL to give the user: the first time it is a 3-day trial for $1, then the plan's monthly price; nothing is charged until they pay there. With a subscription already active it returns a confirm_url, because a switch is prorated and charged to the card right away, and only the billing page may confirm that. none cancels at the end of the paid period, after which sending stops.