I am trying to withdraw an item, but getting error 503

[EnelGy]

api url path : "/exchange/v1/withdraw-assets"
statusCode: 503, {"code":"Unavailable","message":"Service is temporary unavailable."}
I might be putting wrong ids... But if I did that, that wouldn't throw error 503, am I right ? So just to ensure...
the request body should be of this type:
{ "assets": [ { "classId": "string", "gameId": "string", "id": "string" } ], "requestId": "string" }
and I have filled it with
{ "assets": [ { "classId": "244572484:1336167975", "gameId": "tf2", "id": "7c38dbc5-61bc-5e5f-8289-f2b4741d623d" } ], "requestId": "135da4s65d4a" }

1. where do I get requestId (for now I just used some random characters)
2. is id the itemId obtained from item details by dmarket?

Lets skip to the code...

The headers should be good, they are working for example in case of using "/exchange/v1/offers-buy"
So where is the problem ? Am I just putting wrong ids, or the api endpoint is closed ?