Only admins can add billing entities. If you cannot find the relevant billing entities in the drop down please contact your company admin or firstname.lastname@example.org.
If you do not have billing entities set up on Candex, the system would require that you add them or it will not allow you to initiate/accept any payments. You can either add these details yourself or add your finance contact to complete this step for you.
If you want to a new billing entity, from Add a Payment page select Add New next to the billing entity.