Http Monitor Creation is forbidden

I am attempting to create a new Http Monitor using Postman.

I can view our existing monitor via a GET request to https://devicecloud.digi.com/ws/Monitor.

To create the monitor, as per the documentation, I am sending a POST request to the same url using the same auth header, and I am attaching the monitor details to the request body as an XML doc (and including a Content-Type header specifying that). But I get back a 403 Forbidden error with no further details.

I have attempted to create the monitor using an Admin account and using the Owner account to no avail.

The xml being attached looks like:

DataPoint
http
http://myUrl.com/api/digi
json
100
none
ACTIVE
180
Push Monitor for My App
true
POST
30000