Converting Slack-Node welcome app to TS

I am trying to us TS instead of JS. The template im converting is “slack-node”

I have a dist and everything works. except when i run mapps code:push

• when i run it from root app deploys but shows the src app
• when i run it from dist there is an error below

✖ There was an error building application.
  Couldn't detect a valid source code, list of supported languages:
  https://cloud.google.com/docs/buildpacks/builders#buildergoogle-22_supported_languages)