It is simple enough to send a GET request to the url https://apps.fpb.org.za/erms/fpbquerytitle.aspx?filmtitle=&Submit1=Search to get the 1st page of search results of the wesbite.

However, I cannot figure out how to request subsequent pages, which involve sending a POST request to the same url but with a lot form data parameters.

I have managed to get the results of page 2 as follows

with requests.session() as s:

    ### REQUESTING FIRST PAGE

    r = s.request('get', 'https://apps.fpb.org.za/erms/fpbquerytitle.aspx?filmtitle=&Submit1=Search')
    soup = BeautifulSoup(r.content, 'html.parser')


    ### REQUESTING SECOND PAGE

    page_number = 2
    form_data = {
        '__EVENTTARGET': '',
        '__EVENTARGUMENT': '',   
        '__VIEWSTATE': soup.find('input', id = '__VIEWSTATE').get('value'),
        '__VIEWSTATEGENERATOR': soup.find('input', id = '__VIEWSTATEGENERATOR').get('value'),
        '__EVENTVALIDATION': soup.find('input', id = '__EVENTVALIDATION').get('value'),
        'vwfpbquerytitle_DXKVInput': soup.find('input', id = 'vwfpbquerytitle_DXKVInput').get('value'),
        'vwfpbquerytitle$CallbackState': soup.find('input', id = 'vwfpbquerytitle_CallbackState').get('value'),
        'vwfpbquerytitle$DXSelInput': soup.find('input', id = 'vwfpbquerytitle_DXSelInput').get('value'),
        'vwfpbquerytitle_DXHFPWS': soup.find('input', id = 'vwfpbquerytitle_DXHFPWS').get('value'),
        'popupControlWS': soup.find('input', id = 'popupControlWS').get('value'),     
        'DXScript': '1_155,1_87,1_147,1_97,1_123,1_106,1_113,1_84,1_139,1_137,1_98,1_135',
        '__CALLBACKID': 'vwfpbquerytitle',
        '__CALLBACKPARAM': (
            f"c0:KV|777;{soup.find('input', id = 'vwfpbquerytitle_DXKVInput').get('value')};GB|20;12|PAGERONCLICK3|PN{page_number - 1};",
        ),
    }
    r2 = s.request('post', 'https://apps.fpb.org.za/erms/fpbquerytitle.aspx?filmtitle=&Submit1=Search', data = form_data)
    soup2 = BeautifulSoup(r.content, 'html.parser')

But the last response r2 does not give me any indication for what the constantly changing __CALLBACKPARAM and vwfpbquerytitle$CallbackState parameters should be for the next request, as they are not present anywhere in the HTML response. In fact the only reason I can set the __CALLBACKPARAM correctly for the 2nd request above is because I can see by inspecting the website that the patterns such as c0:KV|777, etc. are always there for that 2nd request.

So my question is how can I request subsequent pages past this point? Because setting __CALLBACKPARAM in the previous way, e.g.

page_number = 5
'__CALLBACKPARAM': f"c0:KV|777;{soup.find('input', id = 'vwfpbquerytitle_DXKVInput').get('value')};GB|20;12|PAGERONCLICK3|PN{page_number - 1};"

just gives me the same 2nd page of results as before