One of the easiest ways of losing profit in a business isn't losing a customer. It's forgetting to include the expenses that are incurred for half of your customers.

Individually, they may seem small.
Expense amount
Vendor
Expense date
Category
Receipt
Customer (if billable)
The moment an expense is marked as billable, it can later be added directly to an invoice.

Do employees need to be associated with expenses?
Do you track travel and mileage costs?
Do you need custom fields to capture project or customer information?
How will your team identify billable expenses?
Go to Settings -> Expenses to configure mileage expenses and other expense categories.

Things to Remember
Not every expense needs to be entered manually.
Depending on how your business operates, you can add expenses in different ways:
Create an expense individually as the cost occurs.
Add multiple expenses at once using Bulk Add Expenses.
Import historical expenses from spreadsheets.
Record project-related expenses and associate them directly with customer work.
Track mileage expenses based on distance travelled, GPS tracking, and odometer readings for client visits, installations, and service trips.
Pro Tip: Upload receipts when creating expenses. This creates a helpful audit trail internally and makes it easier to answer customer queries later.
Watch out: Many businesses track expenses but forget to mark them as billable. As a result, the expense gets recorded and the customer gets invoiced, but it never makes it onto the invoice, and that's money left on the table. Every billable expense captured protects your profit margin.
Important Links:
Configure & Manage Expense Category: https://www.zoho.com/invoice/help/expense/expense-tracking.html#expense-categories
Set Mileage Preference: https://www.zoho.com/invoice/help/expense/preferences.html
Record Reimbursements: https://www.zoho.com/invoice/kb/expenses/record-reimbursement-expense.html
Invoicing an Expense: https://www.zoho.com/invoice/help/expense/reimbursable-expense.html