After creating an upstream invoice that bills against a client contract, funding, or prime contract, you can send a copy of the invoice's 'Detail' tab to your upstream collaborator to review. Once reviewed, your collaborator can then reply directly to that message to indicate that they have approved your invoice for payment (or to supply you with a reason for rejecting your invoice). To ensure that your collaborator's response is captured in writing, Procore saves all replies to your outgoing message's 'From' address in the Emails tab on the invoice.