You received the email because you haven't logged into your account in the last 365 days, and haven't used any paid resources with Heroku for the past six months. We will delete your account starting October 26, 2022 if you don't log into Heroku before this date. We will also delete any unpaid apps and add-ons that solely belong to an inactive account.
In addition to our plans for inactive account deletion, Heroku is also ending free Heroku Dynos, free Heroku Postgres and free Heroku Data for Redis plans starting November 28, 2022. You must upgrade your free dynos and data add-ons to paid plans before this date to avoid disruption to your apps or the deletion of data. See our Removal of Heroku Free Product Plans FAQ for more info.
See our blog post and the Removal of Heroku Free Product Plans FAQ for more info related to the ending of free plans and inactive account deletion.