Importing the PlexSign.key

I've had some issues importing the PlexSign.key. I've been running Plex on my Synology 1515+ NAS for months, but realized I should probably add this key. Whenever I try to add the key I get an illegal certificate error.

I followed this guide for the setup. (https://support.plex.tv/hc/en-us/articles/205165858-How-to-add-Plex-s-package-signing-public-key-to-Synology-NAS-Package-Center)