If job approval is switched on, the job will need to be approved before it can be outsourced to the supply chain. The status of the job will be 'Not Authorised' and you can see in the job details who needs to approve the job.
Additionally, check that the Employer has an Agency linked to them for the relevant category of candidate. To check this, locate the Employer through the Main Menu, and select 'Linked Agencies' from the Employer profile tab. Locate the Agency name in the displayed list and expand by clicking 'Categories'. You now check that the specific Agency is configured to supply candidates working within the required category, and so and so can receive Outsourced jobs.