References: https://gist.github.com/pastleo/aa3a9524664864c505d637b771d079c9 https://askubuntu.com/questions/981165/l2tp-ipsec-failing-to-connect-kubuntu-17-10 When run the command to install the package `networkmanager-l2tp 1.2.10-3`, an error occurs like below: $ yaourt -S networkmanager-l2tp … ==> Validating source files with md5sums… network-manager-l2tp-1.2.10.tar.gz … Passed network-manager-l2tp-1.2.10.tar.gz.asc … Skipped ==> Verifying source file signatures with gpg… network-manager-l2tp-1.2.10.tar.gz … FAILED (unknown public key 49A7787EF8D3C039) ==> ERROR: One or more…