Return many to many field queryset as json

I am trying to return all the results of a many to many query (all the customers linked to a store i.e. a customer can be linked to many stores). I have the following models and serializers

class Customer(models.Model):
    stores = models.ManyToManyField(Store)
    first_name = models.CharField(max_length=30, blank=True)
    last_name = models.CharField(max_length=30, blank=True)
    ...

class Store(models.Model):
    store_name = models.CharField(max_length=30, unique=True, null=True)
    ...

class CustomerSerializer(serializers.ModelSerializer):
    stores = serializers.PrimaryKeyRelatedField(queryset=Store.objects.all(), write_only=True, many=True)

    class Meta:
        model = Customer
        fields = ['stores', 'first_name', 'last_name', ...]

In my views, I want to get all the customers in a store and return them like this:

def return_customers(request, *args):
    ...
    store = Store.objects.get(account__email=user)
    customers = Customer.objects.filter(stores__id=store['id'])
    print(customers)
    json_customers = CustomerSerializer(customers).data
    print(json_customers)

    context = {
        'customers': json_customers,
    }
    return Response(context, status=HTTP_200_OK)

This returns an empty object {}

print(customers) gives: <QuerySet [<Customer: Michael>, <Customer: Naomi>, <Customer: Blessing>, <Customer: John>, <Customer: Cena>]>

print(json_customers) gives: {}

If I try to return customers instead of json_customers, I get error message (Type Error): Object of type Customer is not JSON serializable

If I try json_customers = CustomerSerializer(customers[0]).data I get only the first customer (I want all of them):

"customers": {
   "id": 7,
   "first_name": "Michael",
   "last_name": "",
   ...
},

I have tried this with other models that don't have many-to-many fields and it works just fine. I have also added .values() and .values_list() to the end but still returns empty. SOS

customers are multiple.

json_customers = CustomerSerializer(customers).data

change to

json_customers = CustomerSerializer(customers, many=True).data

refer to

https://www.django-rest-framework.org/api-guide/serializers/#dealing-with-multiple-objects