我有以下表格：
forms.py

class TipoDePagoForm(forms.Form):
    tipo_de_pago = forms.ChoiceField(widget=forms.RadioSelect, choices=FORMAS_PAGO, required=True)
    folio = forms.CharField(widget=forms.TextInput(attrs={
        'class': 'form-control',
        'placeholder': 'Folio',
        'aria-describedby': 'basic-addon2'
    }), required= False)
    medio_venta = forms.ModelChoiceField(queryset= MediosVenta.objects.all())

HTML中的ModelChoiceField是这样表示的：

<form method="POST" class="card-body">
              {% csrf_token %}
                <h3>Opciones de Pago</h3>
                  <div class="d-block my-3">
                    {% for value, name in tipodepagoform.fields.tipo_de_pago.choices %}
                    <div class="custom-control custom-radio">
                      <input id="{{ name }}" name="tipo_de_pago" value="{{ value }}" type="radio" class="custom-control-input" required>
                      <label class="custom-control-label" for="{{ name }}">{{ name }}</label>
                    </div>
                    {% endfor %}
                  </div>
                  <div class="d-block my-3">
                    <label for="folio">{{ tipodepagoform.folio }}</label>
                  </div>
                  <div class="d-block my-3">
                    <select name="{{ tipodepagoform.medio_venta.nombre }}" id="{{ tipodepagoform.medio_venta.id_for_label }}">
                      {% for value, name in tipodepagoform.fields.medio_venta.choices %}
                        <option value="{{ value }}" {% if tipodepagoform.medio_venta.value == value  %} selected {% endif %}>{{ name }}</option>
                      {% endfor %}
                    </select>
                  </div>

                  <hr class="mb-4">
                  <button class="btn btn-primary btn-lg btn-block" type="submit" >Pagar</button>
            </form>

在视图（视图的一部分）中执行POST时：

def post(self, *args, **kwargs):
        today = date.today()
        tipodepagoform = TipoDePagoForm(self.request.POST or None)
        
        

        if tipodepagoform.is_valid():
            tipo_de_pago = tipodepagoform.cleaned_data.get('tipo_de_pago')
            folio = tipodepagoform.cleaned_data.get('folio')
            medio_venta = tipodepagoform.cleaned_data.get('medio_venta')
            print(medio_venta)

form_is无效，并显示以下错误：

<ul class="errorlist"><li>medio_venta<ul class="errorlist"><li>This field is required.</li></ul></li></ul>

打印我看到的选择“无”值的表单：

<tr><th><label for="id_medio_venta">Medio venta:</label></th><td><ul class="errorlist"><li>This field is required.</li></ul><select name="medio_venta" required id="id_medio_venta">
  <option value="" selected>---------</option>

  <option value="1">Gimnasio</option>

  <option value="2">Marketplace</option>

  <option value="3">Membresías</option>

</select></td></tr>

我不知道为什么即使我选择了任何带有值的选项，它实际上也没有选择。
打印后：

<QueryDict: {'XXXXXXXXXX], 'tipo_de_pago': ['Efectivo'], 'folio': ['']}>

帖子没有获得模型选择字段