If you are unable to install plugins or themes using the WordPress Upload Zip installer and are seeing a 404 error instead of the plugin or theme being installed successfully then most likely this problem is being caused by the new cPanel ModSecurity Tool (added in cPanel version 62 sometime around Dec 2016). To fix this problem login to you hosting account cPanel > locate the ModSecurity Tool > click the Disable button to disable ModSecurity. You should now be able to install plugins and themes using the WordPress Upload Zip installer.
Recommendation: If you have the BPS or BPS Pro plugin installed then leave ModSecurity disabled. If you do not have the BPS or BPS Pro plugin installed then you may still want to leave ModSecurity disable or you can enable and disable the ModSecurity Tool in cPanel as needed.
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