Generating your Base64-encoded credentials

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: <client_id>:<client_secret>

For the Authorization header value, precede your B64-encoded credentials with the word "Basic " and a space, as demonstrated here:

Basic <B64-encoded_oauth_credentials>