How to add nested fields in request_body_json?

I’m trying to build a custom source connector using Connector Builder UI. The structure of API request should be as follows:

 "id": "1",
 "method": "SerpstatKeywordProcedure.getKeywords",
 "params": {
   "keyword": "iphone",
   "se": "g_us",
   "minusKeywords": ["app", "apple"],
   "filters": {"lang": "en"},
   "sort": {"region_queries_count": "asc"},
   "page": 1,
   "size": 2

I can use Request Body in the UI to set key-value pairs like “id”: “1” but for params object it doesn’t work. Is it possible to set nested objects in API request body in Connector Builder UI?