How to send JSON object as JSON String with Postman?

I want to send a JSON request but problem is I need to send my userPropertiesAsJsonString field as JSON string.

How can I send userPropertiesAsJsonString as JSON string?

{
    "User" : {
        "userId" : "11111",
        "userPropertiesAsJsonString" : ?
    }
}

userPropertiesAsJsonString is;

{
    "properties" : {
        "propertyName" : "test",
        "propertyDesc" : "desc"
    }
}

Try this :

{
    "User" : {
        "userId" : "11111",
        "userPropertiesAsJsonString" : "{\"properties\" : {\"propertyName\" : \"test\",\"propertyDesc\" : \"desc\"}}"
    }
}