Values must be an entity with Status and StatusUpdatedSource attributes.
Have an export mapping for Values entity. I normally prefer to work with MD. But you can choose JSON structure too.
In the Export mapping, you already have an option to work with List or single object.
Pass Values entity to the export mapping and you get the JSON back.
This should work:
{{
"values": {{
"Status": "Cancelled",
"StatusUpdatedSource": "User"
}
}