Many users have reported that they were seeing the 21030 error on their Sky TV when trying to stream content on the Discovery UHD+ app.
At present, the Discovery UHD+ app is said to be the only app giving the following error but we are sure that the error may also come with other apps.
During our research, we found that The Sky TV team is aware of the issue and already working to fix it ASAP.
However, for the time being, a few users have come up with a few walkarounds that have helped them deal with the error and stream on the Discover UHD+ app without the error.

Fixes For Sky TV error 21030
Fix 1: Clear The app cache
Clearing up the app cache or reinstalling the app fresh would do the trick if the error is being caused as a result of an issue with conflicting data in the app cache.
Once you clear the app cache, restart the device and check to see if the error still persists.

Fix 2: Disable HDR settings
Another effective way that has been reported by users would be disabling the HDR settings.
Firstly, update your media streaming device OS to the latest version available. Then, head to the Display and Audio settings, and Disable the HDR settings option from there.
You can also select the “Adaptive” option if you have it available on your device and check if the following issue gets resolved.

Fix 3: Reach out To the Sky Support
If the above workarounds are not helping with the issue then you should reach out to the Sky support team to report the issue. To find the contact details to reach out to the SKY support you can refer here.