I run multiple pinholes using keepalived. Then I only use one DNS in my DHCP server. Second pihole will seemlessly take over if the first one goes down whilst using the original DNS address.
Work quite well. I had to learn the hard way that only using a single pihole was just asking for my partner to be mad when it didn’t work / when I was doing server maintenance. Now I have multiple and they can all seemlessly take over if any my server nodes are down
So return it if you bought a TV like that.
Buy these things with a credit card. If the store refuses a return or demands a restocking fee, credit card dispute. Visa doesn’t fuck around with this stuff.