def METHOD_NAME(self, instance, validated_data):
    now = self.__class__._later_than_func()
    if instance.expiration and instance.expiration < now:  # expired are readonly
        raise serializers.ValidationError(f"Cannot change expired Acknowledgement")
    expiration = validated_data.get("expiration")
    instance.expiration = expiration
    instance.save()
    return instance