This may seem crazy, but check to make sure your model and OS version is compatible. The next thing is to ensure you have the recommended amount of hard drive storage space. That upgrade just so happens to be 2.82Gb. I would reboot my network by unplugging the power cord for about 20 minutes to allow stored memory and voltages to dissipate. Then I would try it again, assuming my model, and OS software version is compatible.
If you're using one of these computers with OS X Mavericks or later, you can install macOS Catalina. Your Mac also needs at least 4GB of memory and 12.5GB of available storage space, or up to 18.5GB of storage space when upgrading from OS X Yosemite or earlier. Learn how to upgrade to macOS Catalina.
If this does not help, your next step should be to reach out to Apple Support.
Best of luck!