Unity RTB error 1001: Invalid JSON format
What Unity Exchange says
The bid response is a malformed JSON.
Unity Exchange reports this integer in the ${AUCTION_LOSS} macro on the bid's lurl. A search for Unity RTB error 1001 is this code.
What to change
The body was not valid JSON. Fix the serializer. A trailing comma, or a string where Unity expects a number, is enough to return 1001.