AJAX and Django, AJAX success not working

In an HTML page I have a table where one can drop items into and that is posted to the server via AJAX as follows:

function drop(ev, el) {
  if (ev.target.tagName=="IMG") { return; }
  var data = ev.dataTransfer.getData("text");

          type: 'POST',
          url: server_url + currentPath,
          data: {
            'version': data
          success() {
            console.log(data, "ranked ");

on the same page, users submit an answer using a button which is linked to a function that sends a POST request to the server:

function NextPage(){
  answer = $("#justification").val();
        if (answer.length < 10){
            document.getElementById("warning1").innerHTML  = "Please provide an answer";
        else {
                    type: "POST",
                    url: server_url + currentPath,
                    data: {'answer' : answer},
                    success: function () {
                        window.location.href =  server_url+ nextPath;


I can read the data from the post request on the server side (i.e., version and answer), and it gets saved as well, but then I cannot move to the next page, and there are no error messages; I noticed that the answer is now passed as a parameter on the URL; not sure what that means. I guess it gets stuck because of an error. I checked the currentPath and NextPath and they are correct. I think the problem is with the ranking object, because when I removed it, everything worked perfectly fine. Can someone spot something I am missing that caused this issue? here is my view:

def task_view(request ,visualisation, task, progress):
    participant = get_object_or_404(Participant, user=request.user)
    question_list = Question.objects.filter(complexity = 'N')

    question = question_list[0]
    answer, created = Answer.objects.get_or_create(participant=participant, question=question)

    ranked_visualisation = SVG.objects.filter(name=visualisation, task=task)  
    if request.method == 'POST':

        participant_answer = request.POST.get('answer')  
        current_version = request.POST.get('version') 
        for i in ranked_visualisation:
            ranking, created = Ranking.objects.get_or_create(participant=participant, svg=i)
            if ranking.svg.version == current_version:
                ranking.ranking = 10
                ranking.ranking = 20
        tasks_completed = participant.tasks_completed
        if participant_answer  and not participant_answer.isspace():
            tasks_completed = tasks_completed +1   
            tasks_completed = tasks_completed
        participant.tasks_completed = tasks_completed
        answer.answer = participant_answer

    context = {'task':task,'question': question, 'answer': answer, 'progress': progress}
    return render(request, 'study/A.html', context)

here are my models:

class SVG(models.Model): 
    name = models.CharField(max_length=200)
    version = models.CharField(max_length=200, default='none')
    task = models.CharField(max_length=200, default='none')
    def __str__(self):
        return self.name
class Ranking(models.Model):
    participant = models.ForeignKey(Participant, on_delete=models.CASCADE)
    ranking = models.IntegerField(default=0)
    svg = models.ForeignKey(SVG, on_delete=models.CASCADE)
class Answer(models.Model):
    participant = models.ForeignKey(Participant, on_delete=models.CASCADE)
    question = models.ForeignKey(Question, on_delete=models.CASCADE)
    answer = models.TextField(blank=True, null=True)
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