Is it possible to refund a full or partial order directly from Shopify with Wallee? Currently, I have to proceed the refunds manually through Wallee.
Yes it is possible
The wallee app must be installed in order to capture, refund and make installments and subscriptions. (Partial payments only work if deferred option is selected.)
About the wallee app:
Where can Shopify customers get the wallee app?
The app is not listed in Shopify: It can only be accessed directly via Shopify integration in Wallee Space. There you will see the option to install/activate the wallee app in Shopify.
Here you can read more about how to refund directly from Shopify: