With Boost Sales, buy one get another for free is never that easy. By creating a bundle of 2 same items, and then apply a half of total price, you have a sweet BOGO offer like this.

Here is the step-by-step instruction to create this offer:
Step 1: In Custom Cross-sell offers dashboard, hit Add offer to get started

Step 2. Enter offer's name and message and select a product twice to bundle them together in your cross-sell offer

Step 3. Add a discount price of item value then hit Save & Submit offer

That's done! Let's boost your sales with the sweet BOGO offer.