Unable to set up a specific request body with extend_schema

[lev-slinsen]

Unable to set up a specific request body with extend_schema.
The description in source files says:

    :param request: replaces the discovered ``Serializer``. Takes a variety of inputs
        - ``Serializer`` class/instance
        - basic types or instances of ``OpenApiTypes``
        - :class:`.PolymorphicProxySerializer` for signaling that the operation
          accepts a set of different types of objects.
        - ``dict`` with media_type as keys and one of the above as values. Additionally, in
          this case, it is also possible to provide a raw schema dict as value.

The first option works, as per the example in documentation. But it's unclear how to set up a custom dict. I've tried multiple different variations and usually it results in 2 options (regardless of my custom fields):

request={"field1": OpenApiTypes.STR, "field2": OpenApiTypes.STR, ...} >>> "string"
Yes, not even a json, just a single word "string".

And in some other cases I've seen this appear:

{
  "additionalProp1": "string",
  "additionalProp2": "string",
  "additionalProp3": "string"
}

Which clearly looks like a placeholder.