post https://gateway.stage.bill.com/connect/v3/network/invitation/vendor/
Send an invitation to connect a vendor created in your organization with a vendor in the network. BILL sends an invitation email to the vendor email address.
When the vendor accepts the invitation, the vendor in your organization is connected with the invited vendor. If the invited vendor does not respond, delete the invitation (with DELETE /v3/network/invitation/vendor/{vendorId}) before sending a new invitation.
Note: If the invited vendor does not respond to an invitation for 60 days, the invitation expires.