check your build output: https://dashboard.heroku.com/apps/a8563fd4-d22f-498e-a510-156f9377ce6e/activity/builds/3e71ec68-15b5-445a-b868-05e8438277b3 code example

Example 1: 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

Example 2: heroku logs

heroku logs --tail