code: def _check_unique_together(cls):
          
          if cls._meta.unique_together is None:
              return
  
          if not isinstance(cls._meta.unique_together, (tuple, list)):
              raise ConfigurationError(
                  "'{}.unique_together' must be a list or tuple.".format(cls.__name__)
              )
  
          elif any(
              not isinstance(unique_fields, (tuple, list))
              for unique_fields in cls._meta.unique_together
          ):
              raise ConfigurationError(
                  "All '{}.unique_together' elements must be lists or tuples.".format(cls.__name__)
              )
  
          else:
              for fields_tuple in cls._meta.unique_together:
                  for field_name in fields_tuple:
                      field = cls._meta.fields_map.get(field_name)
  
                      if not field:
                          raise ConfigurationError(
                              "'{}.unique_together' has no '{}' "
                              "field.".format(cls.__name__, field_name)
                          )
  
                      if isinstance(field, ManyToManyField):
                          raise ConfigurationError(
                              "'{}.unique_together' '{}' field refers "
                              "to ManyToMany field.".format(cls.__name__, field_name)
                          )
docs: Check the value of "unique_together" option.