In your JSON structure, you must provide all the possible fields that your object can contain:
"Questions": [
{
"QuestionNumber": 8,
"QuestionType": 3,
"AnswerData": "{\"BMIvalue\":\"\",\"Height1\":\"5\",\"Height2\":\"6\",\"IsMetric\":false,\"Weight1\": 130,\"Weight2\":\"0\"}",
"IsActive": false,
"Options": [],
"Answers": [],
"Warning": "",
"InfoMessage": "",
"IsFirstWarning": false,
"Id": 36016,
"Name": "BMI Calculator"
}
]
By default, Mendix use the 1st example of what your array will contain. So it took the one without the specification for the field AnswerData.
That’s why this field comes up with the type “unknown”, even if it appears in the 2nd object of the array.
Then, in your export mapping, the field will be empty or not, depending on what will be filled in, no issue.
Try changing AnswerData to a simple string value. Then make sure it is nillable. That should do the trick