The connection to the GPM cannot be established.

I am a newbie with GRAV and just made a fresh installation. Now I wanted to follow the theme tutorial and install the devtools plugin as first step. When I go to +add on the plugins page in admin panel it gives the error message "The connection to the GPM cannot be established". Same with the templates section.... What went wrong?

Start by reproducing the failure from a fresh Grav installation in the Admin panel's Plugins and Templates sections, using the “+add” flow mentioned in the report. Trace the GPM connection error and verify that both sections can retrieve available items without showing “The connection to the GPM cannot be established.”

Written by the indexing model from the issue text.