How to verify ALPINE LINUX 3.9?

Question

linux

I download Alpine Linux standard version.

wget http://dl-cdn.alpinelinux.org/alpine/v3.9/releases/x86_64/alpine-standard-3.9.0-x86_64.iso

There is a GPG key on their website .
GPG 0482 D840 22F5 2DF1 C4E7 CD43 293A CD09 07D9
495A

gpg --verify ncopa.asc alpine-standard-3.9.0-x86_64.iso.sha256

writes that gpg: verify signatures failed: Unexpected error.
How can this be fixed?

Answer 1

But when checking it
gpg --verify ncopa.asc alpine-standard-3.9.0-x86_64.iso.sha256
writes that gpg: verify signatures failed: Unexpected error.

alpine-standard-3.9.0-x86_64.iso.sha256 is just sha256 from iso, there is no signature. The signature should be in a file with the .asc extension behind the "GPG" button, but there is a 404.
Judging by the contents of dl-cdn.alpinelinux.org/alpine/v3.9/releases/x86_64 , there are still signatures for some .iso