问题如下：

unable to render this definition

the provided definition does not specify a valid version field. please indicate a valid swagger or openapi version field. supported version fields are swagger: "2.0" and those that match openapi: 3.0.n (for example, openapi: 3.0.0).

解决办法：

只要在创建FastAPI之后添加一行代码即可

app = FastAPI()
app.openapi_version = "3.0.0" #添加这一行