Install the Bril LSP before using this extension. First, install a Rust toolchain and then run:
cargo install --locked --git https://github.com/ethanuppal/bril-lsp bril-lsp
Once you've installed it, disable and reenable this extension if you already installed the extension.
If there's an LSP crash, let me know immediately via a GitHub issue or some other method. See if restarting the extension fixes the problem.