unknown public key 8F0871F202119294 on ArchLinux

gpg --recv-keys 8F0871F202119294

• the missing key needs to be added to your USER keyring

I did not need to trust the key for makepkg to finish the build.

• ~/.gnupg/gpg.conf also needed:

keyserver-options no-honor-keyserver-url

in my particular case

Keys from AUR are not in the keyrings provided by the distributions' repositories.

You will need to find and add the AUR package/upstream keys manually, if you trust them.

Start by checking the PKGBUILD file of the package, then the comments in the AUR to see where/if to get and add the keys.