I want see on my get request no id of related tables, I try to get the value of colum, but when I tried to do it I got this errors

models.py

PH = "PHONE"
FACE = "FACEBOOK"
EM = "EMAIL"

TYPE_CHOICES = (
    (PH, "Phone"),
    (FACE, "Facebook"),
    (EM, "Email")
)


class Category(models.Model):
    name = models.CharField(max_length=1300)
    img_path = models.CharField(max_length=100)

    def __str__(self):
        return self.name


class Branch(models.Model):
    latitude = models.CharField(max_length=200)
    longitude = models.CharField(max_length=200)
    address = models.CharField(max_length=200)

    def __str__(self):
        return self.address


class Contact(models.Model):
    type = models.CharField(max_length=10, choices=TYPE_CHOICES, default=EM)
    value = models.CharField(max_length=150)

    def __str__(self):
        return self.value


class Course(models.Model):
    name = models.CharField(max_length=200)
    description = models.TextField()
    category = models.ForeignKey(Category, on_delete=models.SET_NULL, null=True,
                                 related_name='courses')  # если удалим поле категории то поле будет Null
    logo = models.CharField(max_length=120)
    contact = models.ForeignKey(Contact, on_delete=models.CASCADE)
    branch = models.ForeignKey(Branch, on_delete=models.CASCADE)

    def __str__(self):
        return self.name

Serializers.py

class CourseListSerializer(serializers.ModelSerializer):
    categories = serializers.SlugRelatedField(slug_field='name', read_only=True)
    branch = serializers.SlugRelatedField(slug_field='address', read_only=True, many=True)
    contacts = serializers.SlugRelatedField(slug_field='value', read_only=True)

    class Meta:
        model = Course
        fields = '__all__'  

Traceback
-----------------

  File "C:\Users\Азамат\AppData\Local\Programs\Python\Python38-32\lib\site-packages\rest
_framework\serializers.py", line 678, in <listcomp>
    self.child.to_representation(item) for item in iterable
  File "C:\Users\Азамат\AppData\Local\Programs\Python\Python38-32\lib\site-packages\rest
_framework\serializers.py", line 529, in to_representation
    ret[field.field_name] = field.to_representation(attribute)
  File "C:\Users\Азамат\AppData\Local\Programs\Python\Python38-32\lib\site-packages\rest
_framework\relations.py", line 533, in to_representation
    return [
TypeError: 'Branch' object is not iterable
[15/Jul/2020 14:36:33] "GET /courses/ HTTP/1.1" 500 121986