I get a bunch of support requests about failed Unity downloads. These are all resolvable with a little perseverance.
The asset download and distribution system is managed by Unity and is beyond our control. It also protects our IP, so we will not make the package available outside of the normal Unity system.
The first thing you need to consider is that Unity downloads your purchases to your Unity content cache before you can install it into your project, which is on your operating systems main disk, so you need to make sure you have enough free disk to download your package.
If you do have enough free space, and there are still issues, then chances are the local .unitypackage is corrupted. Delete it and try the download again.
On Windows the unity content cache is located at:
C:/Users/(your user name)/AppData(hidden)/Roaming/Unity/Asset Store(version)
On a Mac it is located at:
You will then need to navigate to the publisher name e.g. Procedural Worlds
If you do a Google search on this you will find that the question gets asked many times, so if the locations below are incorrect, then try a Google search and select a more recent answer.
Here is a sample Google search for you.
If this still does not help then please lodge a request with Unity Support.
The other issue you might have is a lack of disk space on your projects drive - please see our other article in this section to learn more.