When running a sale it is great to show the old price crossed off. This shows the user that they are getting a deal!
Steps
Go to the Portal and login
Navigate to Configuration > Web Paywall
Go to Products and click on the 3 dots of the product you want to show the crossed off price
Under Sale Options select "Show old price struck out"
Put the Old Price (assuming the "Product Price" is the sale price)
Click Update
Note: When you hit update, it will take a while to update as the system is updating prices for each currency. You can specifically edit this by reading this article on different currencies