Not sure why it would do that? As long as you have permissions setup for the site then it should sign it. I sent you Nostash which is a good iPhone signer developed by nostr:npub1yaul8k059377u9lsu67de7y637w4jtgeuwcmh5n7788l6xnlnrgs3tvjmf Takes a few steps to setup but works well.
Discussion
nostr:npub137c5pd8gmhhe0njtsgwjgunc5xjr2vmzvglkgqs5sjeh972gqqxqjak37w made Nostr Build Shack, which does event signing as well, among other things. It looks pretty slick.
Thank you 🫂🫂🫂