Sounds like you might not have all your dependencies installed, most Node apps will have a Build Command like npm install; npm build;. (or the yarn equivalents if you’re using yarn).
If that’s not it, if you could share some more details of the issue you are experiencing that may help us troubleshoot it with you, e.g. any logs/errors/output, specific URLs, service name/ID, reproduction steps, build/start command, etc.
However, if you don’t want to share these details on the community forum, please feel free to raise a ticket with support@render.com