Issue
You have a provisioned Heroku Postgres instance and credentials have changed.
Resolution
Occasionally we will roll Heroku Postgres credentials, this can happen for several reasons.
Normally this is around maintenance or hardware failures but we also perform credential rolls for security reasons - typically this involves us setting the new configuration variable, DATABASE_URL for primary app databases, and restarting your application. This can cause issues if you have manually copy and pasted these credentials elsewhere, or have hardcoded them into your application.
You can get the new credentials by running this command via the CLI: heroku config or visiting your app's Settings page and clicking the "Reveal Config Vars".
We now let you attach our Heroku Postgres addon to multiple apps as part of the platform and credential updates like this would also update the attached applications. See managing add-ons for more info.