formatter definition not found #431

Installed Neoformat with Plug in Neovim 0.7.2 on Linux Mint 19.3

I can't figure out how to get Neoformat to work with Prettier. I installed Prettier as a snap package in --devmode, so that it wouldn't be sandboxed. I installed node package Prettier globally, and it does show up when I list the global packages with npm list -g. I can use prettier succesfully on the command line.
But in nvim, :Neoformat prettier returns: "formatter definition for prettier not found".
What critical step am I missing?
Tnx