If your Shopify-side refund hasn't reached Amazon, the first thing to check is whether the Refunded orders setting is turned on in the app. When this setting is off, the app will not push any Shopify refund to Amazon — refunds simply stay on Shopify.

Where to check

1. Open Settings in the app's left navigation.
2. Go to Order Settings → Cancelation and Refund.
3. Look for the Refunded orders toggle (its description reads "Sync refunded orders from Shopify to Amazon").

Fix it

If the toggle is off, switch it on and save. From this point on, every refund you create on a Shopify order will be picked up and pushed to Amazon.