In dependency get_service I want to decide by request_type_code which of two services to choose:

from typing import Annotated, Literal
from uuid import UUID

from fastapi import FastAPI, Body, Depends
from pydantic import BaseModel, Field, RootModel

app = FastAPI()


class ProlongService:
    pass


class InclusService(ProlongService):
    pass


def get_service(request_type_code: str = Body()):  # does not work
    if request_type_code == "inclus":
        return InclusService()
    return ProlongService()


class ProlongSchema(BaseModel):
    attachment_ids: list[UUID]
    partner_id: UUID
    request_type_code: Annotated[Literal["prolong"], Field(...)]


class InclusSchema(ProlongSchema):
    region_codes: list[str]
    request_type_code: Annotated[Literal["inclus"], Field(...)]


class CreateSchema(RootModel):
    root: Annotated[InclusSchema | ProlongSchema, Field(..., discriminator="request_type_code")]


@app.post("/create")
async def create(data: CreateSchema, service: InclusService | ProlongService = Depends(get_service)):
    pass

The code above gives wrong swagger schema:

Keys inside data should be one the same level as request_type_code.

How to retrieve only request_type_code into get_service dependency?