I dont have a problem shipping back something which was sent to me in error. If I am getting my money back and they pay the return shipping why shouldn't I send it back to them?
Usually on an error like this they will tell you to discard it or do what ever you like and give you a refund. (Most times they don't ask for you to return it on such a small item as the shipping equals the product value. ) ymmv
I prefer no work
+10, their error they have to fix it. 👍😉