One plan per project, the free trial, the portal, and what a lapsed plan means.
A plan belongs to a project, not to a person. Settings › Billing shows which the project is on, and the card is in Stripe's own portal: FlexOS never sees the number.
A project exists for free, and existing is free: everything it holds stays kept and readable. Flexi works in it while the trial runs, and again once it has a plan.
Each project starts with a free trial of three days, with no card. Start it from the plan screen when the project is made, or from Billing. When the trial runs out and no plan is behind it, the project opens on Billing alone: the site stays live at its address, everything you made stays yours, and Flexi waits until the project has a plan again.
One plan, everything included: Flexi, every agent, your site on a real address, your code on GitHub. Nothing is counted per message. The pricing article has the numbers; the panel shows what your project pays.
Card & receipts opens Stripe's portal for the project: change the card, see the receipts, cancel. A payment that fails is retried by Stripe for days before anything is paused, so one bad card day does not lock a project.
When the owner hands a project to someone on it, that person becomes the owner and pays from then on. A project nobody pays for yet starts its free trial that day.