This could be an indication of a couple of things;
1 - The full installer of Monterey is already in the Applications folder and was corrupted. If that is so, Drag and Drop the Install Monterey to Trash and Empty Trash. Start again with a new download.
2 - There was not enough Empty Space for the Installer to download, expand and install. If upgrading from macOS Sierra or later, your Mac needs 26GB of available storage to upgrade. If upgrading from an earlier release, your Mac needs up to 44GB of available storage.
3 - There is some Third Party Software interfering with the download and or installation process. AntiVirus Software should be removed as per Developers Instructions. They are unneeded, cause havoc and interfere with the normal operation of the OS including the download and installation of Monterey.
There are factors:
1 - Like poor Wifi connection
2 - Slow wifi connection
3 - Too many other people downloading at the same time and Apple Severs are overloaded
4 - Software on the computer interfering with the download process including AntiVirus Software
5 - Running behind a VPN which may increase Packet losses and corrupt the download
6 - If via wifi too many Other devices using the wifi at the same time reducing the Bandwidth to your computer.
7 - Best Results are via Ethernet Cable to Router