Email an invitation into a Workspace the person owns or administers.

Requires the write scope and a role that manages members: the Owner may invite admin, editor or viewer; an Admin may invite editor or viewer (403 for a role the caller cannot grant). The Owner's plan must include team members (Office or Enterprise). The invitee accepts from the email with their own Fintable login, creating one on the invitation page when they have none; the API never sets a password for them. An address that is already a member is refused (409); a repeat for an address with an open invitation replaces it. Rate limited separately: 10 per minute and 200 per day per person, because each call sends an email.