Software update

If one is talking of update to 11.2.1 Try Restarting in Safe Mode - Shift - immediately at startup. If via Wifi - disconnect all other devices using the Wifi. Move as close the Router as possible . If via Ethernet do same - Safe Mode

Should one be upGrading from another macOS perform same.

Please - confirm if the machine is on the List Supplied by Apple as the machine have issue

Shutdown computer. Shutdown Router. Restart Router. Restart computer in Safe Mode. Try Again

What is the exact error message you're getting?

blee55gf wrote:

I have tried that but I still fail

It would help us to help you if you told us what you are trying to update from what to what on what.

Not Sure - but Profile as per original Posters - looks like the 11.2 to 11.2.1

So, what Solved it

Good