brakes takes a vector of specific points not a character string , I think you want to use date_breaks instead. See the documentation.
date_breaks A string giving the distance between breaks like "2 weeks", or "10 years". If both
breaksanddate_breaksare specified,date_breakswins.
If you need more specific help, please provide a proper REPRoducible EXample (reprex) illustrating your issue.