Start adding a card (admin)
Create a card-capture session for the organization and return the client secret the embedded card form needs, plus the publishable key to mount it. The saved method appears (via webhook-verified confirmation) in the payment-methods list and on the billing-account document; it is never inferred from the client-side confirmation alone. Org-admin humans only — service tokens are denied. 403 FEATURE_NOT_ENABLED until the buyer-card-collection flag is on for the organization.
Authorizations
API key or access token
Response
Start adding a card (admin)
Everything the client needs to mount an embedded card-capture form. The resulting payment method is NOT returned here — it appears once the card rail webhook confirms it (spec §6: never inferred from a client callback).