If pkg can’t be installed because missing pkg.txz.pubkeysig, try this:

Go to /usr/local/poudriere/data/packages/13amd64-default/.latest/Latest:

echo -n "$(sha256 -q pkg.txz)" | openssl dgst -sha256 -sign /usr/local/etc/ssl/keys/pkg.key -binary -out ./pkg.txz.pubkeysig