Got this error

Since you're using the custom project type, you must provide the ionic:serve npm script so the Ionic CLI can
serve your project.

Start by checking the custom project type configuration and npm scripts used by the Ionic CLI; the report identifies a missing ionic:serve script but names no file. Reproduce the error in the conference app, determine where that script must be provided, and verify that the CLI can serve the project without the message.

Written by the indexing model from the issue text.