If you haven't already created a fair amount of code that relies on the REST API, I would start off using the GraphQL API. Here is the documentation detailing how a new refund is created --> https://shopify.dev/docs/admin-api/graphql/reference/orders/refundcreate. Although I'm not sure if this endpoint allows the API consumer to pass along a refund reason. Whereas the REST API does appear to include this --> https://shopify.dev/docs/admin-api/rest/reference/orders/refund#create-2020-10.
Hope this helps a little!
I have seen that post, but not sure what to make it.
Is the post suggesting that there is not API method to achieve "Return Items" or I should use "Refund" method ?
I have tried refund method with 0.00 amount. The result is not same as when I use Shopify user interface to do a "Return Items" . May be I am not passing the right parameters.
|From Shopify UI :||From Shopify API :|