If you are using vim-plug, add this in your config files (such as ~/.config/nvim/init.vim), in the call plug#begin() ... call plug#end() section.

Use :PlugInstall and :UpdateRemotePlugins to install, then close and open neovim.

" Using the github repository
Plug 'simsapa/simsapa-neovim'

" Or, if you cloned the repository:
Plug '~/path/to/simsapa-neovim'

Start the Simsapa app, close the main window and let the app stay in the background. The plugin makes HTTP reqests to the application.

Open this README.md file.

Either select or place the cursor on the following word and press Ctrl L: majjhima patipada

It should open a Simsapa Word Lookup window with the results (including Pāli accents).