How to use the Apps build command for static site resources

I have a static site to deploy to Apps as a resource. The source is in the /src folder and I have an NPM launched NodeJS build script that outputs to /dist.

How do I specify my build script in the App Spec build_command property? I tried npm run build which works locally but errors in DO

[2022-09-05 22:32:36] => Initializing build
[2022-09-05 22:32:36] => Retrieving source code to /workspace
[2022-09-05 22:32:36] => Selecting branch "main"
[2022-09-05 22:32:36] => Checking out commit "<redacted>"
[2022-09-05 22:32:36] => Got source_dir: src
[2022-09-05 22:32:36] => Using workspace root /workspace/src
[2022-09-05 22:32:36] 
[2022-09-05 22:32:36] => Building app using buildpacks
[2022-09-05 22:32:36] => Configuring custom build command to be run at the end of the build:
[2022-09-05 22:32:36]      npm run build
[2022-09-05 22:32:36] => Running buildpack detection
[2022-09-05 22:32:36] 
[2022-09-05 22:32:36]    digitalocean/static  v0.0.2  (Static Assets)
[2022-09-05 22:32:36]    digitalocean/custom  v0.1.1  (Custom Build Command)
[2022-09-05 22:32:36] 
[2022-09-05 22:32:36] 
[2022-09-05 22:32:36] => Building app
[2022-09-05 22:32:36] 
[2022-09-05 22:32:36] Running custom build command: npm run build
[2022-09-05 22:32:36] bash: npm: command not found
[2022-09-05 22:32:36] building: exit status 127
[2022-09-05 22:32:36] ERROR: failed to build: exit status 1
[2022-09-05 22:32:36] 
[2022-09-05 22:32:36] 
[2022-09-05 22:32:36]  ! Build failed

Note that some Googling yields this link which leads to a 404 https://docs.digitalocean.com/products/app-platform/concepts/command/