To learn more about PunchOut vendors and how PunchOut works see What is PunchOut

It's possible the user(s) have not been added to the PunchOut Group on Procurify.

To add users to the Procurify PunchOut Group by selecting Edit beside Group Access. Select the user(s) you wish to have PunchOut access by clicking the checkbox beside their name. Once selected click Save then Complete Intregation.