Novel info
Become A Side Character In The World Of The Novel I Read

An office worker was disappointed with the ending of the novel he was reading. Feeling betrayed by the author he made blasphemous words and curses into a message sent to the author's account. At the end of the message he typed.
('I can make a much better ending than the one you fucking author')
After sending the message he fell asleep and what was waiting for him when he woke up was an unfamiliar sky.