See if you have an internet connection. Open your browser, and try to see if you can access any site.
Maybe your network card or Wifi is not detected (I don’t know which one you use, since you don’t indicate anything).
Greetings and take care.
I am sure of my internet connection and I can easily browse the web, but I still see this error, I even installed a package to test using pacman, and I still see the error!
Hi @gnkalk, it would be helpful if you can start the installer by running sudo cnchi-start.sh on a terminal and share the terminal output here when the error occurs. We are also available for live assistance on Discord 
I encountered the exact same errors when I tried to install on my office computer. In my case, it turned out the RebornOS Live image booted up with an IP address that didn’t match my office network; hence, no access to the Internet.
Launch the RebornOS Welcome Application. Then visit the Website (top left corner) or the Wiki (2nd row, 1st column). In my case, both failed because no internet connection. Click on Settings => Wired Connected => Wired Settings. My office PC is using Ethernet. You may need to click on something else if you are using WiFi.
Network Setting Dialog (Sorry, I can upload only one image).
If you do not see an entry in the Network Setting dialog for either a wired or wireless connection, click on the + (add) button. In my case, I clicked on the Setting button.
Wired connection Configuration (Sorry, I can upload only one image)
The IPv4 address, default route and DNS were wrong, not part of my office network. I clicked on “Remove Connection Profile” button at the bottom of the dialog, which returned me to the Network Setting dialog where I clicked on Add.
New Profile dialog (Sorry, I can upload only one image).
Switch to the IPv4 tab of the New Profile dialog. I switched from DHCP to Manual, entered my static IP address, netmask, gateway, DNS servers, and default route details. After that, I went back to the RebornOS Welcome App and found that I was able to access the Website and Wiki. I was then able to continue with the installation.
Good Luck.
In general, it is of course always the case that if DHCP is disabled in the router, the OS cannot obtain an IP address and it always has to be configured manually. That has nothing to do with RebornOS. 