Statuscode 400 on TS/JS but 200/Success on Python

[SteamUs1]

When I try to sell an item on the community market with Typescript, I always get a 400 although it totaly works on python.

 

  This is my Python code:

session = requests.Session()

cookies = {
        "sessionid": "XXX",
        "steamLoginSecure": "X%7C%XX.X.X",
    }

session.cookies.update(cookies)

def sellSteamMarketItem(cookie):
    url = "https://steamcommunity.com/market/sellitem/"

    HEADERS = {
        "Referer": "https://steamcommunity.com/profiles/XXXXXX/inventory"
    }
    session_body = session.post("https://steamcommunity.com/market/sellitem/", data={
        "sessionid": "XXXXX", 
        "appid": "730",                          # App-ID (z. B. CS:GO)
        "contextid": "2",                        # Kontext-ID (Inventar)
        "assetid": "XXXX",                # Artikel-ID
        "amount": "1",                           # Anzahl
        "price": "149999"                        
    }, headers=HEADERS)

   if session_body.status_code != 200:
       print("Error, Statuscode: ", session_body.status_code)
   

 

And this is my Typescript code:

create(assetId: number, price: number) {
        let url: string = "https://steamcommunity.com/market/sellitem/";
        const data = {
            sessionid: this.session.sessionid,
            appid: "730",                          
            contextid: "2",                       
            assetid: assetId.toString(),               
            amount: "1",                          
            price: price.toString(),                      
        };
        const referer = "https://steamcommunity.com/profiles/" +  this.session.client.steamID.getSteamID64() + "/inventory";
        const respone = this.session.steamAPI.httpPost(url, data, referer);
        console.log(respone);
        //this.session.community.acceptConfirmationForObject(this.session.identitySecret, respone["listingid"], )
    }

async sendRequest(url, method, params, referer, repeated=false) {
	const headers = {
                        "Cookie": this.session.cookies, 
                        "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36",
                        "Accept": "application/json, text/plain, */*",
                        "Accept-Encoding": "gzip, deflate, br",
                        "Connection": "keep-alive",
                        "Referer": referer
                    };
	this.response = await axios.post(url, params, {
                            headers: headers
                        });
}

Here some Sequences from the Axois Request:

{
  "headers": {
    "Accept": "application/json, text/plain, */*",
    "Content-Type": "application/json",
    "Cookie": "sessionid=XX; steamLoginSecure=XX;",
    "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36",
    "Accept-Encoding": "gzip, deflate, br",
    "Connection": "keep-alive",
    "Referer": "https://steamcommunity.com/profiles/XX/inventory",
    "Content-Length": "123"
  },
  "method": "post",
  "url": "https://steamcommunity.com/market/sellitem/",
  "data": {
    "sessionid": "XX",
    "appid": "730",
    "contextid": "2",
    "assetid": "XX",
    "amount": "1",
    "price": "14555"
  }
}


{
  "data": {
    "success": false,
    "message": "Session mismatch"
  },
  "status": 400
}

 

Has anyone an idea, why this occurs?

Edited Sunday at 06:22 PM by SteamUs1

[SteamUs1]

I found the issue. Its in the Content Type, in Python its "application/x-www-form-urlencoded" and in TS its "application/json". 
To get the same Type in Python you simply need to format the params (body) right. For example:

const data = new URLSearchParams();
data.append('sessionid', sessionid);
data.append('appid', '730');
data.append('contextid', '2');