src/Core/CoreConstants.php
public static function getAccessTokenFromArray(array $settings){
        if(array_key_exists('accessTokenKey', $settings)){
            return $settings['accessTokenKey'];
        }else if(array_key_exists('accessToken', $settings)){
            return $settings['accessToken'];
        } else if(array_key_exists('AccessToken', $settings)){
            return $settings['AccessToken'];
        } else{
            return null;
        }
    }
public static function getAccessTokenFromArray(array $settings){
        if(array_key_exists('accessTokenKey', $settings)){
            return $settings['accessTokenKey'];
        }else if(array_key_exists('accessToken', $settings)){
            return $settings['accessToken'];
        } else if(array_key_exists('AccessToken', $settings)){
            return $settings['AccessToken'];
        } else{
            return null;
        }
    }
A helper method to get Access Token Key. People may have a typo on the key name
@param Array $settings     The array contains all the key values
@return String | null      The access token developer provided