'HTTP POST request - different requests return same response

I'm trying to retrieve data from a site by sending a POST request which appears to work, however, it returns the same result despite the request changing.

For example, if I change the dates, it will still return the same result and if I check this via the website manually, it should be different.

Any help would be greatly appreciated! I'm stuck with this.

Bdate = 20210220
Adate = 20220220   

#Prepare the column headers
BdateVal = str(Bdate) + " Est. value ($m)"
AdateVal = str(Adate) + " Est. value ($m)"

#retrive payload and enter index + dates
d =  {"__EVENTTARGET":"m$m$p1$p1$ITrakResults$DownloadButtoniTrak",
      "__EVENTARGUMENT":"",
      "__LASTFOCUS":"",
      "__VIEWSTATE":VS,
      "__VIEWSTATEGENERATOR":VSG ,
      "__SCROLLPOSITIONX":0,
      "__SCROLLPOSITIONY":0,
      "m$m$p1$p1$ITrakFilter$ddlInvestmentIn":352,
      "m$m$p1$p1$ITrakFilter$ddlComparisonPeriod":Bdate,
      "m$m$p1$p1$ITrakFilter$HiddenFieldLatterDate":Adate,
      "m$m$p1$p1$ITrakFilter$txtInvestorName":"",
      "m$m$p1$p1$ITrakFilter$ddlInvestmentStyle":"",
      "m$m$p1$p1$ITrakFilter$ddlInvestorList":"All Company Lists",
      "m$m$p1$p1$ITrakFilter$ddlInvestmentTrends":0,
      "m$m$p1$p1$ITrakFilter$slider_min":0,
      "m$m$p1$p1$ITrakFilter$slider_max":71000,
      "m$m$p1$p1$ITrakFilter$txtSliderLeftValue":0,
      "m$m$p1$p1$ITrakFilter$txtSliderRightValue":71000,
      "m$m$p1$p1$ITrakFilter$ucLocation$Location":"RadioButtonLocationIgnore",
      "m$m$p1$p1$ITrakFilter$ucLocation$DropDownRegions":0,
      "m$m$p1$p1$ITrakFilter$ucLocation$DropDownCountries":0}

params = {"InvIn":352,
          "FormerDateID":Bdate,
          "Holders":0,
          "ShowDetail":"True",
          "InvName":"",
          "sort":"LatterEstMarketSegmentValue",
          "sortAsc":"False"}
   
#Post request
GetCSV = s.post("https://secure.somewebsite.com/iTrak/Default.aspx?",params=params, headers=DownloadHeaders, data=d)