Create various Company-Users and assign them to different roles like Billing, Sales and Support for greater control over processes handled by each department. For example, the Billing department can be assigned rights for Adding Funds, handling Invoice & Credit Transactions, etc. but will be restricted from performing any action on Support related issues such as Technical Modification and Assistance, etc. The Company-Users can be created from your Control Panel by going to Settings >> Company Users >> Add.
You then need to fill up the form and designate the Billing, Sales or Support or a combination of the three roles to the concerned Company User. Modifications can also be made to the role of a Company User at any time in future by going to Settings >> Company Users >> Rights & Permissions >> Set Menu Permissions. Do refer to our Managing Company User Knowledgebase for more details.