Hello I get the same problem on macOS and I don't know how to move past it. Can someone tell me where I made a mistake? Here is what I get when I try to enter the command to obtain the signing key
macos ~ % curl -O https://releases.grapheneos.org/allowed_signers
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 104 100 104 0 0 851 0 --:--:-- --:--:-- --:--:-- 852
MOD NOTE: User opened dedicated thread / duplicate https://discuss.grapheneos.org/d/35198-signify-error