I see your solution is working (with your JSON) but with mine I get validation errors:
Error: Parse error on line 4:
...ate", "payload":"{"id":"5d8e31ea6bd1135
----------------------^
Expecting 'EOF', '}', ':', ',', ']', got 'undefined'
This is why I escape mine - my endpoint seams to have no problems with the escaped JSON. As a side note, my JSON is also valid if I not need to put it in this structure.