Invalid command ProxyRequests when setting up jenkins

You should enable proxy. Run a command:

 sudo a2enmod proxy
 sudo /etc/init.d/apache2 restart

proxy module must be disable. Enable it using below command

a2enmod proxy

If you don't have access to root, you can use

sudo a2enmod proxy

After that restart apache server using

service apache2 reload

 sudo a2enmod proxy
 sudo a2enmod proxy_http
 systemctl restart apache2

If you don't enable proxy_http you get this error in the apache error log file for the site:

AH01144: No protocol handler was valid for the URL / (scheme 'http'). If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule.