Actually, the default update process fetches the pack from a server and serves you the file. And 403 error refers to access forbidden from the server. So, somehow your htaccess or server isn't allowing the URL to fetch the file from a remote server. Maybe for some security purpose.
So, in this case, you need to download the file manually from the served URL http://prntscr.com/og42xy and install it manually.
BTW, did you try to recopied and pasted the license key into Page Builder Options, and clear the Joomla and browser cache, please?
Best Regards