There's a few reasons why this is happening:
- The code snippet that was placed on your returns page, didn't have the "myshopifyURL" changed to your shopify URL.
- Your orders numbers use special characters or letters. For example some stores use the # in the order number such as #1001 or letters SA1001. The customer will need to enter it the way you have your store formatted. You can access those settings in the "General" tab of your Settings page.
- The order was placed before the app was installed. You can fix that by clicking here!
- The order was just placed and will not be search-able for 5 minutes.