A salary sacrifice is an arrangement between you and your employee which enables your employee to pay for certain goods or services straight from their pre-tax salary. The effect is to reduce an employee’s taxable income and subsequently their tax liability.
For a salary sacrifice to be permissible, both you and the employee need to be in agreement. Bike to work and travel passes are the two most common uses of a salary sacrifice. More information about each of these is available here:
SimplePay has a system item for salary sacrifices for each of these. You can read more about using these system items in the following help articles: