Using the old API loading of materials is not supported anymore. This means the plugin could be broken on server versions before 1.13 using the whitelist feature. However it should work fine from now on using every new materials added from this update up to the next ones.

Maybe that using the "LEGACY" prefixed item in the materials list could work temporarily in versions prior to 1.13 but it is deprecated in the api and should not be used! I do not plan to make this plugin working on previous versions of 1.13 because I do not think a lot of you are using it. If it is usefull for you I will try to provide a fix for that though.