So after I get an authorization code successfully returned from the Mailchimp OAuth2 API, I try to do a getAccessToken, and get an "invalid_request" error returned.

I'm implementing the call as described in the PHP League docs for the parent library:

$client = new \CFreear\OAuth2\Client\Provider\MailChimp(
                array(
                    'clientId'          => $client_id,
                    'clientSecret'      => $client_secret
                )
            );

$token = $client->getAccessToken('authorization_code', array(
                    'code' => $authorization_code
                )
            );

I'm able to start the client and connect to the Mailchimp API, and do everything up to this point successfully.

I've also verified that you've got the correct https://login.mailchimp.com/oauth2/token endpoint defined for the getAccessToken call.

I'm kind of at a loss since all of my credentials are correct and work otherwise. Additionally the PHP League OAuth2 library works on every single other OAuth call I'm making to other services.

Thanks!