check your build output: https://dashboard.heroku.com/apps/84af43a7-1f7b-4e33-b392-ebe780ee9ffb/activity/builds/4ebc60fe-88e2-4728-bc0c-d531e2d98774 code example

Example 1: heroku logs

heroku logs --tail

Example 2: heroku logs

# Display all logs live
heroku logs -t -a YOUR_APP_NAME

# Only display stdout of your app
heroku logs -t -s app -a YOUR_APP_NAME