1. Navigate to Your Shopify Admin > Settings > Checkout
2. Scroll down to the Post-purchase page section. Choose UpsellPlus Checkout Offers.
3. Click 'Save'!
Here's a quick gif of how to do this:
That’s it. Once saved, the offer will appear for your customers.
Shopify has some limitations and considerations for the post-purchase page, you can read about them here.
The main restrictions are that a post-purchase offer won’t work with: