The above page instruction say to use "PUT" but when using PostMan and "Put" I get the following:
405 Method Not Allowed
If I change the method to "POST" I get 200 OK with an export of data on what has been changed, but yet, I don't see these changes within the HubSpot portal.
I am unable to reproduce that. When using PUT I get a 200 OK response and the deal is updated as per the documentation. If I try to do a POST I get a 405 METHOD NOT ALLOWED. Are you also encoding the body in JSON? See my postman examples below: