Hi there,
Thanks for reaching out.
We usually see this kind of issue when the install step is missing from the Build Command, are you installing the dependencies before trying to run them? For example, a Build Command should probably be something like:
npm install; npm build;
If your dependencies are in devDependencies of the package.json you may also need to check they’re being installed as the NODE_ENV can change what is installed. npm install docs
Hope that helps
Alan