If you have an expense that is billable back to a customer, you can track it using Versa. First activate the setting "Track expense and items by customers." from Setup menu, Bills.
When you are entering a bill item, you would see an option to mark it Billable. Check the checkbox and you can specify the amount to bill back to the customer and the customer to bill to. The system will remember this so you can bill back the customer later.
Go to Invoices menu, Pending Billable Expenses to see a list of un-invoiced billable expense items. Click on Create Invoice for each customer listing to create an invoice for that customer.
Or you can just create a new invoice for a customer, when entering an invoice item, choose from the list Billable Expense Item . Choose this will create a new invoice item for this billable expense item