PayPal OAuth: 400 Error even after specifying Host

PayPal OAuth: 400 Error even after specifying Host

I'm doing this one in golang, and I've been up just about the entire night
trying to get it to work. My latest frustration is that I'm getting a 400
error despite the numerous headers I've dropped into my request.
29 req.SetBasicAuth(app.id, app.secret)
30 req.Header.Set("Host", "www.sandbox.paypal.com")
31 req.Header.Set("Accept", "application/json")
32 req.Header.Set("Accept-Language", "en_US")
33 req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
34 req.Header.Set("Connection", "close")
I have auth set up, and every header I could think to add. I've pored over
the documentation and have tried the poke it to see if it works approach
as well. Heres the information I've been passing in the body
`{"grant_type": "client_credentials", "content-type":
"application/x-www-form-urlencoded"}`
If you need some more of the code just tell me. But I'm not super sure
it'll be a whole lot of good. I wanted to make the post as general as
possible as well.