I'm attempting to update Spotify to the latest version in the AUR. Pamac informs me that this version requires libopenssl-1.0-compat and libcurl-openssl-1.0. Here's what happens when the libopenssl-1.0-compat make process begins:


Making package: libopenssl-1.0-compat 1.0.2.k-3 (Sat Apr 22 16:38:40 EDT 2017)
==> Checking runtime dependencies...
==> Checking buildtime dependencies...
==> Retrieving sources...
-> Downloading openssl-1.0.2k.tar.gz...
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 5184k 100 5184k 0 0 5580k 0 --:--:-- --:--:-- --:--:-- 5575k
-> Downloading openssl-1.0.2k.tar.gz.asc...
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 455 100 455 0 0 1138 0 --:--:-- --:--:-- --:--:-- 1140
-> Found no-rpath.patch
-> Found ssl3-test-failure.patch
==> Validating source files with sha256sums...
openssl-1.0.2k.tar.gz ... Passed
openssl-1.0.2k.tar.gz.asc ... Skipped
no-rpath.patch ... Passed
ssl3-test-failure.patch ... Passed
==> Verifying source file signatures with gpg...
openssl-1.0.2k.tar.gz ... FAILED (unknown public key D9C4D26D0E604491)
==> ERROR: One or more PGP signatures could not be verified!

How can the key issuer be notified about this problem?

I found a solution to what has turned out to be a makepkg PGP signature verification problem, installed libopenssl-1.0-compat, and updated Spotify without further issues. In case another newbie encounters this problem,the solution is to enter this command in a terminal window: gpg --recv-keys <Public Key> where Public Key is the one that is reported as "unknown" to makepkg.