Your ambassadors have the option to be email only users meaning they do not need an Apostle account or the Apostle app on their phones. They can share posts occasionally via email. In terms of billing, email-only users will be considered normal users to whom you can suggest posts, and you will be charged accordingly.
On the other hand, for pending invites, you will not incur any charges. This is because you cannot suggest social media posts to individuals whose invitations are still pending.