You might check out this post: Unable to update FTL with pihole -up; sudo apt-get update also did not resolve it. It's a common problem with the OS as the repos are shuffled around and new ones release.
You might check out this post: Unable to update FTL with pihole -up; sudo apt-get update also did not resolve it. It's a common problem with the OS as the repos are shuffled around and new ones release.