How are you downloading it @kzlz?
What program is telling you that the signature is not OK, is it rpm, is it gpg?
I suspect that if the key used for signing the template wasn’t added to the rpm keyring, then rpm would fail to verify the signature (and default to the safer option of assuming it is not OK).
See the begining of this post of you suspect that’s the issue you’re facing:
(You’ll need to use the key that was used to sign the Kali template, which may not be the same as the ine used for the templates in that thead!)