当我点击联系卖家按钮，然后它打开网页，它显示网页不可用网页在什么应用程序：//发送/？电话= 923424627671&text = Hi%2C%20I%20am%20感兴趣的%20in%20the%20产品%3A%0A%0A产品%20名称%3A%20Electric%20%0A产品%20图像%3A%20https%3A%2F%2Ffirebasestorage.googleapis.com%2Fv0%2Fb%2Fecommerce-1b43e.appspot.com%2Fo%2Fimages1677497513119374%3Falt%3Dmedia&type =电话号码& app_absent = 0无法加载，因为：
net：：ERR_UNKNOWN_URL_SCHEME在控制台中，当我点击链接时，它会转到WhatsApp的网页，当我点击继续聊天时，它会发送消息，但在物理移动设备中，它会给出上述错误或网页视图添加是mendory？而在应用程序中，当我点击返回时，它会显示WhatsApp的网页一会儿，但它不会永久打开为什么？有人能解决这个错误吗？这里是我的代码

String buildWhatsAppMessage() {
    String message = 'Hi, I am interested in the product:\n\n';
    message += 'Product Name: ${widget.productName}\n';
    message += 'Product Image: ${widget.url}\n';
    message += 'Product Price: ${widget.productPrice}\n\n';
    message += 'Please let me know more about it.';
    return Uri.encodeFull(message);
  }
  void launchWhatsApp() async {
    String phoneNumber = 'https://wa.me/${widget.phonenumber}?text=${buildWhatsAppMessage()}';
    if (await canLaunchUrl(Uri.parse(phoneNumber))){
     launchUrl(Uri.parse(phoneNumber));
   } else {
     showDialog(context: context,
         builder: (BuildContext context) {
           return AlertDialog(
             title: Text('Seller has no WhatsApp number'),
             content: Text('Unfortunately, the seller does not have a WhatsApp account.'),
             actions: [
               ElevatedButton(
                 child: Text('OK'),
                 onPressed: () {
                   Navigator.of(context).pop();
                 },
               ),
             ],
           );
         });
   }
  }

RoundedLoadingButton(
              child: Text(
                'Contact with seller',
                style: TextStyle(color: Colors.white),
              ),
              controller: contact,
              resetDuration: Duration(seconds: 3),
              resetAfterDuration: true,
              width: 200,
              height: 50,
              color: Colors.blue,
              successColor: Colors.blue,
              borderRadius: 10,
              elevation: 3,
              onPressed: _isAddToContactLoading
                  ? null
                  : () async {
                setState(() {
                  _isAddToContactLoading = true;
                });
              launchWhatsApp();
                  setState(() {
                    _isAddToContactLoading = false;
                  });
                  _addCartController.success();

              },
            ),