This article explains how to publish your products and collections to the Swap sales channel in Shopify.
The returns portal can only see products and collections that are published to Swap, so you need to do this before you can offer Exchange for Something Else (EFSE).
Publish products to the Swap sales channel
Go to your Shopify admin.
Click Products.
Click the product you want to publish.
Open the Publishing drop-down menu.
Click Manage sales channels.
Select Swap.
The screenshot shows a test store, so your list of sales channels will look different.
Click Done.
Publish collections to the Swap sales channel
Publish collections to the Swap sales channel as well as products. The returns portal reads your catalogue through Shopify's Storefront API, which only returns collections published to the channel making the request.
This matters for product-level discounts configured against a collection. If the collection is not published to Swap, the portal cannot see that an exchange item belongs to it, so the discount is not carried over to the exchange. See Understanding how discounts carry over to exchanges (Returns V2).
To publish a collection, open it in Shopify, then under Publishing, add the Swap sales channel.