External Invites: An External Invite is used when you are inviting somebody to a Contract who is not part of your Organization. To send an External Invite, click on "Invite Other Party" on the sidebar of your Contract Document.
Internal Invites: An Internal Invite is used to invite somebody from your own Organization to collaboration, review, edit or sign a Contract. Internal invites are useful to loop in someone in your company so they get notifications about what's happening. When sending an internal invite, you have an option to ask them to Watch, Review or sign this contract. If a user does not already have access to view the contract, internally inviting them will give them access. To send an internal invite, click on "Invite Colleague" on the sidebar of your Contract Document.
Internal users must have User Permissions within the Coupa platform user management to be invited to a contract. If their name does not display when entered in the internal invite then they should contract the Coupa Admin for access to the Coupa platfom.
See the related guides linked below for more details on both External and Internal contract invites.