Change the billing address or VAT id of a self-serve org — during signup (the Company step resubmits here after Stripe refused a VAT id) and after activation, from the Billing details card. A managed org's details stay a superadmin's to set through /activate.

Whether the VAT id is offered at all is the client's call (Stripe takes an EU VAT id only, and the country list lives there); this checks the shape and lets Stripe judge the number itself.