You can display discounted product prices for your invoices by following the simple steps below.
Step 1: Open Simple Invoice from your Shopify store’s “Apps” section.
Step 2: Click on the “Templates” on the Simple Invoice dashboard.
Step 3: Click on the Options section, scroll down and click on the Show Strikethrough Non-Discounted Product Prices under the Line Items.
Step 4: Click on the Save button.