If the Approve section within the Invoice Register is missing, check the following:
Click System, then click Options, then click Invoice Register Options.
Select the Use Advanced Approval checkbox.
If it is already selected, the issue is with the FinOps configuration. Follow these steps:
Open Fin Ops Admin, then click System Control, then click Security Profiles.
Click Edit on the security profile of the user.
Click the Security tab.
Click Authorisation, then click Invoice Register and ensure it is selected.