How do I schedule an AWS Lambda cron to run at 11:30pm on the last day of the month?

I'd like my Lambda function to run on the last day of every month at 11:30pm.

I'm using the Serverless Framework so all I need is the right Schedule Expression (docs here & info here)

Any help greatly appreciated.

NB: Unfortunately I can't just do it at the start of the month as there's a dependency on pulling data from a 3rd party tool that only calculates data for 'this month'.