Cannot use Upfront and not install Themes

Hi there

This is the message I get in my plugin area:

Unfortunately, we do not seem to have Upfront core installed on this site. We need that for the Upfront Builder plugin to work. Get it here.

When I try to install an Upfront theme I get this message

Installation of spirit failed. Most likely reason for this are wrong folder permissions of your wp-contents folder.

Thank you very much for your help.

Kind regards

Armin