8.5 Credits and billing portal

SMS/Email credits are bought on this page (dedicated cards) and never expire — they're used
after the plan's monthly allowance runs out (chapter 6.3).
If you have an active subscription, the Manage billing button opens the Stripe portal
(payment methods, invoices).
When switching plans with an active subscription, the unused time is credited to the next
invoices (Stripe proration) — the screen explains this before you confirm.