Emacs: Failed to verify signature archive-contents.sig : <p>Recently tried to update emacs packages and got this.</p>

<pre><code>Failed to verify signature archive-contents.sig:
No public key for 066DAFCB81E42C40 created at 2019-10-02T10:10:02+0100 using RSA
Command output:
gpg: Signature made Wed 02 Oct 2019 10:10:02 AM BST
gpg:                using RSA key C433554766D3DDC64221BFAA066DAFCB81E42C40
gpg: Can't check signature: No public key
</code></pre>

<p>Any ideas why?</p>
