Error Response: The extension of the URL specified with "Download a Package" > "Package URL" or the extension of content_url specified with content_list.json may not be .pkg/.PKG.Check that the URL extension of the content is .pkg/.PKG
Solution: Unplug your PS4 and plug it back. To turn on the PS4 into Safe mode, Press and Hold down the power button on the PS4, until the console beeps twice. Connect your controller with a cable and select "Rebuild Database". If this doesn't solve your problem, try contacting Sony directly or a video game repair shop for further help. Please post below if you were able to solve the issue yourself to help others.