Send data in non-custom fields - eviltoast

I have a self-hosted ntfy instance and I am gradually building a bare-bones mobile app to display my notifications.

I am publishing by POSTing as JSON. Is it possible for the ntfy server to send all the data fields that are included in the JSON? I would like to pass data in custom fields. Makes sense?

If this does not exist, is it possible to make a feature-request?