It should be:
<Location /plexrequests>
ProxyPass http://localhost:3000/plexrequests
ProxyPassReverse http://localhost:3000/plexrequests
AllowOverride All
Require all granted
</Location>
it’s missing the AllowOverride ALL
in the /etc/apache2/sites-enables/plexrequests.conf file.
The is causing it to require authentication to QB before you hit PlexRequests.