With Boost Sales, buy one get another for free is never that easy. By creating a bundle Cross-Sell of 2 same items, and then apply a half of total price, you have a sweet BOGO offer like this.
Step 1: In Custom Cross-sell offers dashboard, hit Add offer to get started
Step 2. Select a product twice to bundle them together in your cross-sell offer
Step 3. Enter other necessary information of your offer to complete the offer creation
Done! Let's boost your sales with the sweet BOGO offer.