For my products, I need a calculation that will subtract 1 product cost

For my products, I need a calculation that will subtract 1 product cost if 3 products are selected to purchase. Buy 3 get one Free.

You should be able to achieve this with Form Calculation widget.

Can you please try to add the widget on your form and then try to follow the guide step by step?

If you still need assistance, please provide the link or the name, so we can check it and suggest a solution.

We will wait for your response.