In order to set up eBay refunds in StoreFeeder you will need to have "Managed Payments" enabled on your eBay account. You can find out how to do this by visiting eBay's help guide here: https://www.ebay.co.uk/help/selling/getting-paid/introducing-managed-payments-ebay?id=4795
Once you've set up managed payments on eBay, you'll need to make sure you are connected to eBay's new API in StoreFeeder. If you open your eBay integration, you'll notice there are two sections in which you can connect your eBay account to StoreFeeder; you will need to connect each of these, as shown below, in order for eBay refunds to work.
Once all that's done, the 'Managed Payments' toggle on your eBay integration should turn on automatically (shown below). If it doesn't turn on automatically, it might be that eBay have not yet activated managed payments on your account yet, it's not instant unfortunately!
Using eBay Refunds
To refund an eBay order, or part of one, you'll first need to find it in the manage orders grid and then edit it.
Once you're on the 'Edit Order' page, you'll see an option on the left-hand side of the page for 'Channel Refunds', click that.
Once you've clicked the tab, you'll be taken to a page that summarises any existing refund activity against the order you've chosen. This is also the page on which you can create refunds; simply click the green '+ Create Refund' button toward the top right of the page to get started and you should be greeted with this window.
From here you can select which order lines you'd like to refund by using the checkboxes on the left side of each product SKU or simply enter an amount you would like to refund in the 'Order Level Refund' section.
Once you're happy with the amount that you're going to be refunding, click the 'Refund' button in the bottom right of the window to process the refund.