Here are step-by-step guide to check why you did not see the data from the target device using a Cpanel (website of user control panel) or using Viewer app on YOUR device.

1.  Check if the features are turned on or not

Someone forgets to turn on the features they want to track. The application has many features such as GPS tracking, SMS messages tracking, call history tracking, URL (Mobile browser) history, ... but sometimes they turned off and they forget to turn it on. So please login to your account at the control panel website (CPanel) and then you can see on the top-right menu 'Settings', click on that, and select 'Sync Settings' it will show all features supported.
Notes: in some secure/secrete/InPrivate/Incognito user control panel sites, the settings you can see in the menu Device Settings -> Data Delivery -> Change application Settings.
Tick on what features you want to track an then click Save & Sync to make the changes.

2.  Check if your account is still active (not expired yet)

When the account gets expiration and it will be limited to received data log from the target device. So that no data in the control panel site.

Please visit the session about Payment/License to make a purchase.

3.  Check if the target device has an internet connection

The target device does not have the internet connection 100% the time. So that maybe it delay to flush the data log to the server (user control panel) and then it makes you are not able to see the data. So be patient, wait for some hours or even the whole day to see the data.
Wait until the target device has an internet connection, the data will be sent immediately.

4.  The app hangs or stuck

If you have a chance to reboot the target device, please do it.

Or, maybe you should wait until the device has no battery and it will automatically reboot when it was plugged into a charger.

Notes: There are some "essential settings" you should check if the app suddenly stops working. Visit our support site and then you can easily see these links.

More check list for an Android target device

Check if your device is rooted or not

Notes: This checking is for Android devices, but for some features only. See the list of features need android device rooted:
What is rooting and how to root an android

But do not worry, only some features need to have full access to Android OS so it needs rooting. More than 50% of the features do not need to root. Without rooting it still works well.

Check essential settings

(Statistics: 65% met this case)
In case you still keep in your hand the device, please check with the below link to know all essential settings. You can choose by your target device (brand) and version of Android from the session Technique Support -> For Android or you can search keywords "essential settings" or go to the session "Essential settings" or something like that you will see may some articles about how to configure these settings on specific Android version/brand/device.

Maybe an installation again is required if you did not follow the essential settings as above.