This system wide Refunds Default setting in weintegrate controls whether QBO or Shopify assigns the transaction number in QBO for the Shopify refunds document being posted.
This dropdown is preset to QuickBooks Online, but you may opt to change it to Shopify.
If you set this value to QuickBooks Online, then QBO will auto-assign the Refund Receipt number based on your current setting within QBO.
If you set this value to Shopify, then the Refund Receipt number in QBO will be populated with the Shopify refund transaction number.
The Refunds Default screen is available in both the Configuration Setup Wizard and the Connection management section of the app.
Click here to learn about setting the Transaction Date default for integrating with QuickBooks Online.