The Financial role 'Approver' allows a you to set a user to approve Purchase Invoice Register invoices in the Approve Application without having access to the Accounts data.
Before the user is set as an Approver they must first be assigned the appropriate permissions in Financials and this can be done as follows:
In the Members area, locate the user, click on the pop over button in the top right hand corner of their record and select Manage Roles.
In the Financials appropriate dataset, choose User and Save Changes.
Go to Financials and set the relevant Approval Permissions for the user
Return to the Members area and repeat steps 1 - 3 setting the role to Approver.