QNAP Ubuntu 20.04 failing to install

Hi, first off I’m totally new to this so please forgive any transgressions.
I have a QNAP TS253A that I’m trying to install Ubuntu 20.04 on. I think it’s LXC. It gets to 60% then fails with an error message “Could not connect to DNS server (”. I have not the faintest idea where to start solving this problem. Can anyone give me some pointers please.
Thank you, Bryn