private function generateRequestHeaders($signedMessage)
    {
        // Prepare request Http Headers
        $requestHeaders = [
            CurlRequestHandler::YOTI_AUTH_HEADER_KEY . ": {$this->authKey}",
            CurlRequestHandler::YOTI_DIGEST_HEADER_KEY . ": {$signedMessage}",
            CurlRequestHandler::YOTI_SDK_IDENTIFIER_KEY . ": {$this->sdkIdentifier}",
            'Content-Type: application/json',
            'Accept: application/json',
        ];

        if ($version = Config::getInstance()->get('version')) {
            $requestHeaders[] = self::YOTI_SDK_VERSION . ": {$this->sdkIdentifier}-{$version}";
        }
        return $requestHeaders;
    }