The Payables Account screen allows you to store information related to your account with the contact. Account Payables is found under the Payables section labeled Account as seen in the icon below.

The screen view below show the main Accounts Payable window.

Vendor Taxation Number- Any Taxation Numbers for Vendors can be stored here. Multiple Taxation Numbers can be added by clicking the New Tax # icon.

Your Account Information- The Customer's Account number can be stored here. A built in calculator is in the Square Footage field so you can enter in any square footage relevant for this Customer's Inventory.