Hello Adrian,
Thank you for the feedback.
Actually, you don't need the parameter. One of the current parameters of the SendNotification Action is the "Notification". This parameter receives a structure, and in that structure you have a field just for that.
However, there is a bug in the API, and that parameter is ignored.
We will add a fix to this issue in the next version of the component, to be released soon.
Cheers,
Samuel Jesus