В Django customize form форма не отправляла данные на заднюю сторону

Я пытаюсь настроить ModelMultipleChoiceField в форме, но когда я пытаюсь отправить форму, я получаю ошибку Enter a list of values

my form.py

class AppointmentCreateViewForm(forms.ModelForm):
    patient= forms.ModelChoiceField( queryset=Patient.objects.all(),label="Patient")
    appointmentDate = forms.DateField(label="Appointment date", widget=forms.DateInput(format='%Y-%m-%d'))
    appointmentType = forms.ChoiceField(choices=AppointmentTypes, required=False, label="Appointmen type")
    appointmentStatus = forms.ChoiceField(label="Appointment Status", choices=AppointmentStatuss)
    operation = forms.ModelMultipleChoiceField(widget=forms.Select(attrs={
                'class': 'js-example-basic-multiple',
                'name': 'states[]',
                'multiple': 'multiple'
            }), queryset=Operation.objects.all(),label="Operation")
    class Meta:
        model = Appointment
        fields = ('patient', 'appointmentDate', 'appointmentType','appointmentStatus','operation')

мой html

<section>
     <form action="" method="post">{% csrf_token %}
         {{ form.as_p }}  
         <input type="submit" value="Save" />
        </form>
    </section>

my operation model.py

class Operation(models.Model):
    operationName = models.CharField(max_length=255)

    
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)


    def __str__(self):
        return self.operationName


    
    def get_absolute_url(self):
        return reverse('operations')

Вернуться на верх