The system allows contractors to get paid based on their work for an organization.

Many clients pay contractors when they send an invoice for the services they have completed and a printed contractor report from IINSIGHT (case notes section )

As a Contractor (with contractor permissions) they can select the specific billings they will invoice for, which is what is printed in the contractor report. Once selected they cannot be re-selected so contractors cannot bill for the same service twice:

Accounts (with Accountant permissions) then log in and can see all of the costs that a contractor has selected and the accountant marks these costs as now having been paid to the contractor so accountants cannot pay a contractor for the same service twice) :

Therefore you can not have both of these permissions assigned to one user for this reason, the system will only allow you to have one of these permissions assigned.