Chat Engine Docs: Custom JSON

Chat Engine's Custom JSON fields let you embed unique data into any Chat Engine object. This allows you to send an receive data unique to your app's experience.
Rest API tutorial: • Chat Engine Docs: Rest...
Rest API docs: rest.chatengin...

[@100fuegos2]

What is wrong with the PATCH users request, the custom_json in the example of the postman collection or other examples returns always "Not a valid string.", How to fix this?.