Django rest framework m2m post

I am getting an error when posting to one of my endpoints. Error text:

"<Customer: person@example.com>"

must have a value for the field "customer"

before the many-to-many relationship is used.

The client model is configured to be related to the m2m address model, with the addition of empty / null / default = None to make it optional.

If in the serializer I comment out the billing address field, my message succeeds and a new client is created.

I tried several payloads, where I quote the billing address how null

, []

and ""

to no avail.

Models

class Customer(TimeStamped):
    # required
    email = models.EmailField(max_length=255, unique=True)
    has_agreed_to_terms = models.BooleanField(default=False)
    ## extras
    # system id
    user = models.OneToOneField('vauth.User', related_name='customer', blank=True, null=True, default=None)
    # email preferences
    subscription_type = models.CharField(max_length=255, blank=True, null=True, default=None)
    unsubscribed_date = models.DateTimeField(blank=True, null=True, default=None)
    email_frequency = models.CharField(max_length=255, null=True, blank=True, default='Weekly')
    # addresses
    billing_addresses = models.ManyToManyField('common.Address', related_name='billing_addresses_set', blank=True, null=True, default=None)
    shipping_addresses = models.ManyToManyField('common.Address', related_name='shipping_addresses_set', blank=True, null=True, default=None)
    # time stamps
    date_joined = models.DateTimeField(default=timezone.now, db_index=True)
    first_purchase_date = models.DateTimeField(blank=True, null=True, default=None, db_index=True)
    last_purchase_date = models.DateTimeField(blank=True, null=True, default=None, db_index=True)
    # purchases
    number_of_purchases = models.IntegerField(default=0)
    # braintree
    braintree_id = models.CharField(max_length=255, blank=True, null=True, default=None)

      

        
        
        
      

    

serializers

class CustomerSerializer(serializers.HyperlinkedModelSerializer):
    user = serializers.HyperlinkedRelatedField(view_name='user-detail', required=False)
    billing_addresses = serializers.HyperlinkedRelatedField(many=True, view_name='address-detail', required=False)
    # shipping_addresses = serializers.HyperlinkedRelatedField(many=True, view_name='address-detail', required=False)

    class Meta:
        model = Customer
        fields = (
            'url', 'id', 'email', 'has_agreed_to_terms', 'user', 'billing_addresses', #'shipping_addresses',
            'subscription_type', 'unsubscribed_date', 'email_frequency',
            'date_joined', 'first_purchase_date', 'last_purchase_date', 'number_of_purchases', 'braintree_id',
        )