How do I get a Django multiple select form to pass through selected items as a list?

I have a Django application where I use multi-select with dynamic choices as related to the logged-in user, but when I try to submit the form, I keep getting the following error message:

"TypeError at /masstext.html Field 'id' expected a number but got <QueryDict: {'customers': [''], 'textmessage': ['test'], 'csrfmiddlewaretoken': ['FNawscd4CXqtDWIUrq0Kolq3x6R699lStaykXwxDbtqciJortBm0pTfPWSvvjW7L']}>"

I'd like to have it where, when the user submits the form, a new model instance is created with the selected customers and the message typed out as fields. I don't understand why I'm not getting a list of selected customers from the multi-select returned in the list, but rather an empty list.

Code below:

Model:

class Masstext(models.Model):
    profile = models.ForeignKey(Profile, on_delete = models.CASCADE)
    message = models.CharField(max_length = 500, null = True)
    customers = models.CharField(max_length = 1000, null = True)

Form:

class Textform(ModelForm):

    def __init__(self, user, *args, **kwargs):
        super(Textform, self).__init__(*args, **kwargs)
        self.fields['customers'] = forms.ModelChoiceField(
            queryset = Customers.objects.filter(facility__profile__email = user))

    class Meta:
        model = Masstext
        fields = ['customers','message']

View:

@login_required(login_url="login/") def load_customers(request, *args,
**kwargs):
    msg = ''
    if request.method == 'POST':
        user = request.user
        form = Textform(request.POST)
        if form.is_valid():
            form.save()
        
        else:
            msg = "Fields are not valid"

    else:
        form = Textform(request.user)
    
    context = {'form': form}
    return render(request,'home/masstext.html',context)

Template:

<form action="masstext.html" method="POST">
                        {% csrf_token %}
                        <!-- Form -->
                                    <label for="customers">Select Customers:</label>
                                    <br>
                                    <select name="customers" style="height: 250pt" multiple>
                                      {% for customer in form.customers %}
                                      <option value='{{customer.id}}'{{customer}}></option>
                                      {% endfor %}
                                    </select>
                                    <br><br>
                                    <textarea name="textmessage" rows="4" cols="75" placeholder="Write the text message you'd like to send to all tenants selected above here...">{{customer.message}}</textarea>
                                    <br><br>
                                    <input type="submit" value="Submit"> 
                        </form>
                        <!-- End of Form -->