private function getAccessTokenFields($code)
    {
        $this->oAuthFields = [
            'grant_type' => 'authorization_code',
            'code' => $code,
            'redirect_uri' => $this->mpRedirectURL,
            'client_id' => $this->mpClientId,
            'client_secret' => $this->mpClientSecret,
        ];

        $this->fieldCount = count($this->oAuthFields);

        return $this->oAuthFields;
    }