Return Incorrect Value for Function: OrderSubTotalDiscountInclTax & OrderSubTotalDiscountExclTax

We were deploying some pixel at the order confirmation page and need to return the Subtotal amount that is after the discount amount is taken into account. We tried both the functions below and the return values are all 0 for some reason.

OrderSubTotalDiscountInclTax { get; set; }
OrderSubTotalDiscountExclTax { get; set; }

The checkout page shows the correct amount though.

For example, the subtotal before tax, shipping and discount is $180,  the discount is $20,  we should get a return value from the above function of $160+tax, and $160, respectively. However, the return value of both

OrderSubTotalDiscountInclTax { get; set; } & OrderSubTotalDiscountExclTax { get; set; } is 0.

Is this some bug or we miss something ? Thank you.