Heroku removed the free tier so it's best to remove it from the tutorial extensions as participants cannot follow through the tutorial without paying for Postgres. See the message below from Heroku:
It is important to note that Heroku ended free product plans for Heroku Dynos, Heroku PostgreSQL and Heroku Data for Redis on November 28, 2022 (announced in this Heroku blog post). Even after logging back into your account, you will now need to upgrade data resources and dynos using free plans to avoid any data loss or service interruptions.
Heroku removed the free tier so it's best to remove it from the tutorial extensions as participants cannot follow through the tutorial without paying for Postgres. See the message below from Heroku: