Unfortunately, Loupe is no longer available on Pluto. 

You can also continue to enjoy Loupe Art + Music on Samsung TV, LG Channels, Vizio Watchfree, Vix (Prende), Xumo, and others. View the FULL LIST here. Loupe is also available as a TV app you can download for free from the Amazon Fire, Apple TV, Android TV (Google Play), and LG App stores.

You can reach out to Pluto's customer service team at: https://support.pluto.tv/hc/en-us