Django formset show raw data in POST but never gets valid

I have the following Django structure. I use the latest Django version 5.1.

I aim to get Formset working for the first time. Anyway, whatever I tried my formset is never valid. I can see raw data in request.POST but it does not validate therefore I never get parsed data in cleaned_data. What am I missing ?

Model.py

class Folder(models.Model):
    reference = models.CharField(max_length=64, null=False, unique=True,)

class Revenue(models.Model):
    folder = models.ForeignKey(Folder, null=False, on_delete=models.RESTRICT,)
    amount = models.DecimalField(max_digits=10, decimal_places=2, null=False,)

Form.py

class FolderForm(forms.ModelForm):
    class Meta:
        model = models.Folder
        fields = ['reference']

class RevenueForm(forms.ModelForm):
    class Meta:
        model = models.Revenue
        fields = ["amount"]

RevenueFormset = inlineformset_factory(
    models.Folder, models.Revenue, RevenueForm,
    validate_min=True, extra=1, can_delete=True
)

View.py

class FolderTestView(LoginRequiredMixin, UpdateView):

    template_name = "core/folder_test.html"
    model = models.Folder
    form_class = forms.FolderForm

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context["revenue_formset"] = forms.RevenueFormset(instance=context["object"])
        return context

    def post(self, request, *args, **kwargs):
        print(request.POST)                            # Contains whole form raw data
        formset = forms.RevenueFormset(request.POST)
        print(formset.is_valid())                      # Always set as False
        return super().post(request, *args, **kwargs)

    def form_valid(self, form):
        print(form.cleaned_data)                       # Never gets the formset data
        return super().form_valid(form)

    def get_success_url(self):
        return reverse("core:folder-test", kwargs={"pk": self.kwargs["pk"]})

url.py

urlpatterns = [
    path('folder/<int:pk>/test/', views.FolderTestView.as_view(), name='folder-test'),
]

folder_test.html

    <form action="{% url 'core:folder-test' object.id %}" method="POST">
        {% csrf_token %}
        {{ form|crispy }}
        {{ formset.management_form }}
        {% for revenue_form in revenue_formset %}
            {{ revenue_form|crispy }}
        {% endfor %}
        <input type="submit" value="Submit" class="btn btn-primary">
    </form>

<form action="{% url 'core:folder-test' object.id %}" method="POST">
    {% csrf_token %}
    {{ form|crispy }}
    {{ revenue_formset.management_form }}
    {% for revenue_form in revenue_formset %}
        {{ revenue_form|crispy }}
    {% endfor %}
    <input type="submit" value="Submit" class="btn btn-primary">
</form>