         failure: ((Error) -> Void)? = nil,
         success: @escaping () -> Void)
     {
+        // construct header parameters
+        var headers = defaultHeaders
+
         // construct REST request
         let path = "/v1/customizations/\(customizationID)/words/\(word)"
         guard let encodedPath = path.addingPercentEncoding(withAllowedCharacters: .urlPathAllowed) else {

            method: "POST",
            url: serviceURL + encodedPath,
            credentials: credentials,
            headerParameters: defaultHeaders,
            contentType: "application/json",
            queryItems: nil,
            messageBody: body
        )


            method: "GET",
            url: serviceURL + "/v1/pronunciation",
            credentials: credentials,
            headerParameters: headers,
            queryItems: queryParameters
        )

        // execute REST request
