When you have trouble implementing Qiita --devise confirmation email RubyDoc - Module: Devise::Models::Confirmable
It's almost as written here, and the Devise reference is also written.
User.find(1).send_confirmation_instructions # manually send instructions
--The mail was not sent due to some problem on the mailer side. --Worker stopped and lost queue for sending emails
Etc. are possible. It tends to occur during operation, so how do you resend it every time? I was looking into it, so I wrote it.