CMake in NixOS with Catch2

Does anyone have any experience with using these 3 together? I have a project that I am trying to get to work but NixOS is giving me fits because it tries to pull Catch2 from github and because of how it does that, results in an error about Catch2 either not being found or github not being found depending on how I built the flake. I have since moved to another method by pulling Catch2 and putting into a subdirectory and having CMakeLists.txt use add_subdirectory to include it, but that also is giving me fits. Any suggestions please?