Did you manually construct the nostr URL? I think you are using the wrong identifier. The easiest way to ensure you have it right is by looking it up on gitworkshop.dev/repos
nostr://npub1m3xdppkd0njmrqe2ma8a6ys39zvgp5k8u22mev8xsnqp4nh80srqhqa5sf/nostr.thesamecat.io/Alexandria
What platform are you on?