How fix the package "%@"is missing or invalid

I have Downloaded update thrice time

Downloaded what ?

Software update macOS Big Sur.... (version 11)
how to fix it.

May have a look here:
https ://osxdaily. com/2020/11/12/macos-big-sur-update-download-errors/

“The package %@ is missing or invalid” Error Message
Some users have encountered an error message stating  “The package %@ is missing or invalid” when attempting to download or upgrade to macOS Big Sur.
This problem can sometimes be resolved by installing any available system software updates on the Mac first.
Also, sometimes changing the wi-fi network (or turning off wi-fi if you’re on ethernet), and then deleting and re-downloading the macOS Big Sur installer can sometimes resolve the error.

1. i have only single wifi option there is no ethernet port in MacBook Air (13-inch, Early 2014) and this is working on version 10.15.7 (19H1030)

2. sometimes resolve the error.

your sometimes take how many days because i have already spent 2 days on it. and as per internet speet its take almost 6-8 hours

Sir this is my humble request please fix it asap.

I cannot tell how long it would take. I found this reference to the same issue, with some advice, but I could not test it by myself.
For 1 they propose to turn off wifi and then on again (but I doubt that could be the cause).

This seems a more elaborate advice: https://discussions.apple.com/thread/252431443
Here are their advice:

First, make sure all external devices are disconnected before trying to install. Then let's start to macOS Recovery and use Disk Utility to repair the hard drive. Here's how: How to repair a Mac disk with Disk Utility
After the repair is complete, restart your Mac normally. Then you'll want to delete the macOS Big Sur install file and download it again. The install file can be found in the Applications folder and the Launchpad. If you're using any security software, be sure to disable or temporarily remove it so it doesn't interfere with the connection and download.

May check also that you have no firewall :
Some seem to have succeeded by starting in safe mode.
read all ideas here : https://developer.apple.com/forums/thread/649819

Unfortunately, I'm not from Apple, there is nothing I can do to fix it.
Wish all this will finally help.