One hypothesis,
Because the URL you are trying to reach is not available from the RStudio Cloud server. This happens if your URL is resolved from your company name server on the desktop, but the name server is not available on the RStudio Cloud server.
Depending on your level of comfort with server administration, you can modify dhcp client resolution with something like
sudo su
echo "prepend domain-search \"thedomainofyourcompany.extension\";" >> /etc/dhcp/dhclient.conf
echo "prepend domain-name-servers 1.1.1.1, 1.1.1.2;" >> /etc/dhcp/dhclient.conf
dhclient -r; dhclient
Where you replace the domain with the one the URL and the IPs with the one your company uses as name servers.