You pay by card without leaving the site. The card form is put there by Stripe inside the page itself: those details never pass through our servers at any point.
The invoices
Every charge generates an invoice with its number and a downloadable PDF, in the organisation's name and with its CIF (tax ID). The tax details are entered once from the billing screen and changed whenever you need to. In the list, each invoice shows as paid, open or void: a void one isn't owed, which is why it isn't shown as outstanding.
The card
It's saved when you take out a plan and can be changed whenever you like. Changing it charges you nothing: it's validated and kept for the next invoices. It's the same one auto top-up uses, if you have it switched on.
If a renewal charge fails, the plan's credits stop being spent until the subscription is up to date again. Any you bought in a top-up are still yours: they were paid for separately and don't depend on the monthly payment.
Billing is only seen and touched by whoever administers the organisation. The credit balance is visible to anyone on the team, because you need it before asking for an analysis.
The price of each plan is on the pricing page and summarised in the plans.