Downloading the installer build manifest failed.

I have a Macbook Air 2013, running on Yosemite. Attempt to upgrade to Sierra in the past failed and I gave up. Now I am trying to upgrade to Big Sur. Download seems ok, but when I try to install, I keep getting this error message 'Downloading the installer build manifest failed.' I have tried to delete and redownload the installer, and have made more storage space, but still getting the same error message. I need to update now as a few programs require it. Any advice? Thanks in advance!