It says I have to add an amount of timeout to it, so I did that but got "Null" in return. And after a few attempts I get "Method not found" with an error code.
That means that it worked. walletpassphrase will return null when it is successful. If it is not successful, you will get an error.Thank you so much! The single quotes and misunderstanding null was the problem, at last I received my privkey.