Here’s the one to use.
In there, you can define variables that you accept as input. Like in your case, variables can be NoteContent, StartDate etc. Define their types as well.
Configure your Math node and subsequent steps to use those variables from the “Trigger” menu of variables.
Then, from where you’re triggering the webhook, if you’re using a Trigger Webhook node in another action, those variables will show themselves for you to tie data to. If you use an external method, I think you just need to define them in the API call body.