To authorize an API request, set the value of the Authorization header to the Base-64 encoded value of your application's OAuth credentials (if you don't have your application's client ID and client secret , see Getting your OAuth credentials).
Before encoding the credentials, combine them by listing the client_id value, a colon, then the secret value.
In other words, Base64 encode the following: <
For the Authorization header value, precede your B64-encoded credentials with the word "
Basic " and a space, as demonstrated here: