I cant able to install the MacOs Catalina

1. You probably need to check if you have enough space on the drive or volume for installation. The macOS Catalina update will take more than 4.9 GB in total.
2. You may not install to this volume because the Macintosh HD is not mounted when installing macOS Catalina, then you need to check your startup disk in Disk Utility.
3. You can boot your Mac into Safe Mode and reinstall macOS 10.15.

Still unable to upgrade to macOS Catalina because of the error "macOS Catalina could not be verified", even though you have cleared out your content caching and re-download for times? This post would be helpful.

How to upgrade to macOS Catalina.

Before You Upgrade macOS

1. Fix any problems before upgrading.
2. Run First Aid in Disk Utility while booted from your Recovery HD.
3. Backup. Make a bootable clone using CarbonCopy Cloner or use TimeMachine.
4. Be sure your startup disk has 18-20GB of free space during the installation.
5. Upgrade third-party software for compatibility. See App Compatibility Table - RoaringApps. If you have mission critical software, then DO NOT upgrade until you know that software is compatible with the version of macOS you are about to install.
6. Disconnect all third-party peripherals.
7. Download the installer which will be in the Applications folder. Quit the installer after it opens, then make a copy of the installer and save it in the Downloads folder. The one in the Applications folder will be deleted after a successful installation.
8. The download is large, anywhere between 5 and 9GBs. It takes time to complete. Be patient.
9. Double-click on the installer in the Applications folder. Click on the start button to begin the installation.

Look at my Item 4 where I tell you this information.