Altru - /constituentnotes - value for author_id

https://developer.sky.blackbaud.com/api#api=alt-conmg&operation=CreateConstituentNote

When creating a constituentnote, what value does one use for author_id?

I've tried using the Application User recordID (which can also be obtained via ‘Application User Record’ in an ‘Application User’ query) to no avail