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

            return
        }

        // construct REST request
        let request = RestRequest(
            method: "POST",
            url: serviceURL + "/v1/customizations",
            credentials: credentials,
            headerParameters: defaultHeaders,
            acceptType: "application/json",
            contentType: "application/json",
            queryItems: nil,
            messageBody: body
        )


        failure: ((Error) -> Void)? = nil,
        success: @escaping (Voices) -> Void)
    {
        // construct header parameters
        var headers = defaultHeaders
        headers["Accept"] = "application/json"

        // construct REST request
        let request = RestRequest(
            method: "GET",
            url: serviceURL + "/v1/voices",
            credentials: credentials,
            headerParameters: headers
        )

        // execute REST request
