Invite a user to one of the agency's client companies.
Creates a pending invitation and sends an email.

The invitation is sent on behalf of a company user, who is named as the inviter in the email and on the page where the invitation is accepted.
By default this is the company owner. Use inviterUserId to send it on behalf of another company user. That user must have permission to manage users in the company, otherwise a 400 validation error is returned.
If the company has no owner, inviterUserId is required and a 400 validation error is returned when it is omitted.

Scope: agency-users:write