CANNOT get a CRM card to populate with data

Hello! Neophyte developer here.

I cannot get my properties to render in my CRM card.
I’ve created the app, and the card, authenticated it, it appears in the CRM in the right place, the function it’s calling works and the App monitoring greenlights each call.

But nothing appears.

Even when the only property on the card is a string called test and the JSON payload generated and returned - following the documentation - is:

 response_json = {

 "properties": [
 {
 "label": "test",
 "dataType": "STRING",
 "value": "test"
 }
 ]
 }

 return response_json

The card is just blank:

Please help :disappointed_face:

The official documentation is **bleep**, this guy’s video solved it for me: