Django Allauth: How to add more custom fields on signup form?

So, I'm trying to make a custom signup form while using Django allauth on my project. I've reached their documentation and tried to apply it on my code.

In my forms.py I've put this:

class MyCustomSignupForm(SignupForm):
    cpf_cnpj = forms.CharField(max_length=14)
    first_name = forms.CharField(max_length=30)
    last_name = forms.CharField(max_length=30)

    def save(self, request):

        # Ensure you call the parent class's save.
        # .save() returns a User object.
        user = super(MyCustomSignupForm, self).save(request)

        # Add your own processing here.
        user.first_name = self.cleaned_data['first_name']
        user.last_name= self.cleanedD_data['last_name']
        user.cpf_cnpj = self.cleaned_data['cpf_cnpj']
        user.save()
        # You must return the original result.
        return user

I've put the ACCOUNT_FORMS = {'signup': 'mysite.forms.MyCustomSignupForm'} in settings.py as required too.

As you can see on the image linked below, it saves to the user their first and last name, but it doesnt save the cpf_cnpj field Value. What should I do to save this to the user?

in your forms.py add the fields like this to add an extra field in default user creation form provide by django

from django.contrib.auth.forms import UserCreationForm
class MyCustomSignupForm(UserCreationForm):
    email = forms.EmailField(max_length=254, required=True, help_text='Required. Inform a valid email address.')
    cpf_cnpj = forms.CharField(max_length=14)
    first_name = forms.CharField(max_length=30)
    last_name = forms.CharField(max_length=30)

    class Meta:
        model = User
        fields = ('username', 'email', 'cpf_cnpj', ' first_name', 'last_name', 'password1', 'password2', )

and acc to that change you views.py

from .forms import *

def register(request):
    if request.method == 'POST':
        form = MyCustomSignupForm(request.POST)
        if form.is_valid():
            form.save()
            return redirect('accounts:login')
    else:
        form = MyCustomSignupForm()
    return render(request, 'register.html', {'form': form})

urls.py

 path('register/',views.register,name='register'),