old_contents: from rest_framework import serializers
  from silver.models import (MeteredFeatureUnitsLog, Customer, Subscription,
                             MeteredFeature, Plan, Provider)
  
  
  class MeteredFeatureSerializer(serializers.ModelSerializer):
      class Meta:
          model = MeteredFeature
          fields = ('name', 'price_per_unit', 'included_units')
  
  
  class PlanSerializer(serializers.ModelSerializer):
      metered_features = MeteredFeatureSerializer(
          source='metered_features',
          many=True, read_only=True
      )
  
      class Meta:
          model = Plan
          fields = ('name', 'interval', 'interval_count', 'amount', 'currency',
                    'trial_period_days', 'due_days', 'generate_after', 'enabled',
                    'private', 'product_code', 'metered_features')
  
  
  class SubscriptionSerializer(serializers.ModelSerializer):
      trial_end = serializers.DateField(required=False)
      start_date = serializers.DateField(required=False)
      ended_at = serializers.DateField(read_only=True)
      plan = serializers.HyperlinkedRelatedField(
          source='plan',
          view_name='silver_api:plan-detail',
      )
      customer = serializers.HyperlinkedRelatedField(
          source='customer',
          view_name='silver_api:customer-detail',
      )
  
      class Meta:
          model = Subscription
          fields = ('plan', 'customer', 'trial_end', 'start_date', 'ended_at',
                    'state')
          read_only_fields = ('state', )
  
  
  class SubscriptionDetailSerializer(SubscriptionSerializer):
      metered_features = MeteredFeatureSerializer(source='plan.metered_features',
                                                  many=True, read_only=True)
  
      class Meta:
          model = Subscription
          fields = ('plan', 'customer', 'trial_end', 'start_date', 'ended_at',
                    'state', 'metered_features')
          read_only_fields = ('state', )
  
  
  class MeteredFeatureUnitsLogSerializer(serializers.ModelSerializer):
      class Meta:
          model = MeteredFeatureUnitsLog
          fields = ('metered_feature', 'subscription', 'consumed_units',
                    'start_date', 'end_date')
  
  
  class CustomerSerializer(serializers.ModelSerializer):
  
      class Meta:
          model = Customer
          fields = ('customer_reference', 'sales_tax_percent', 'sales_tax_name')
          depth = 1
  
  
  class ProviderSerializer(serializers.ModelSerializer):
  
      class Meta:
          model = Provider
  
new_contents: from rest_framework import serializers
  from silver.models import (MeteredFeatureUnitsLog, Customer, Subscription,
                             MeteredFeature, Plan, Provider)
  
  
  class MeteredFeatureSerializer(serializers.ModelSerializer):
      class Meta:
          model = MeteredFeature
          fields = ('name', 'price_per_unit', 'included_units')
  
  
  class PlanSerializer(serializers.ModelSerializer):
      metered_features = MeteredFeatureSerializer(
          source='metered_features',
          many=True, read_only=True
      )
  
      class Meta:
          model = Plan
          fields = ('name', 'interval', 'interval_count', 'amount', 'currency',
                    'trial_period_days', 'due_days', 'generate_after', 'enabled',
                    'private', 'product_code', 'metered_features')
  
  
  class SubscriptionSerializer(serializers.ModelSerializer):
      trial_end = serializers.DateField(required=False)
      start_date = serializers.DateField(required=False)
      ended_at = serializers.DateField(read_only=True)
      plan = serializers.HyperlinkedRelatedField(
          source='plan',
          view_name='silver_api:plan-detail',
      )
      customer = serializers.HyperlinkedRelatedField(
          source='customer',
          view_name='silver_api:customer-detail',
      )
  
      class Meta:
          model = Subscription
          fields = ('plan', 'customer', 'trial_end', 'start_date', 'ended_at',
                    'state')
          read_only_fields = ('state', )
  
  
  class SubscriptionDetailSerializer(SubscriptionSerializer):
      metered_features = MeteredFeatureSerializer(source='plan.metered_features',
                                                  many=True, read_only=True)
  
      class Meta:
          model = Subscription
          fields = ('plan', 'customer', 'trial_end', 'start_date', 'ended_at',
                    'state', 'metered_features')
          read_only_fields = ('state', )
  
  
  class MeteredFeatureUnitsLogSerializer(serializers.ModelSerializer):
      class Meta:
          model = MeteredFeatureUnitsLog
          fields = ('metered_feature', 'subscription', 'consumed_units',
                    'start_date', 'end_date')
  
  
  class CustomerSerializer(serializers.ModelSerializer):
  
      class Meta:
          model = Customer
  
  
  class ProviderSerializer(serializers.ModelSerializer):
  
      class Meta:
          model = Provider
  
subject: Update the serializer for Customer to display all the fields.