☒ I haven't had this use case yet, but it makes sense. Have a look at https://devcenter.heroku.com/articles/amazon-rds. It worries me though that they're saying to open the database up to the entire world. It is a security risk in my opinion.

Just to make sure, in your ApplicationRecord class, did you set the connects_to?

connects_to database: { writing: :primary, reading: :follower }

I don't know if there is a good way to test localhost without something like ngrok.

It's pretty hard to tell  ☒ . During the discovery of creating this episode, I got that kind of message a few times, but nothing in the error pointed me in the right direction to resolve it. I searched the Apple developer forums a few times and found several hints to resolve the issue and one of them finally worked. However, the kind of error message I got was with the handshake and it prevented authenticating the user. I haven't seen this particular case where you are authenticated, but still get that flash message.

 ☒ You shouldn't have to use Bootstrap with FullCalendar. This issue that you're experiencing is likely due to the changes in Stimulus. They changed the path to "@hotwired/stimulus" instead of "stimulus" when importing the library.