Online generator always indicates that the Swagger is not valid

Description

I wanted to use the online generator to generate codes. I'm using the Zuora swagger definition but whichever file I choose, it always returns this message:

{"code":1,"type":"error","message":"The swagger specification supplied was not valid"}%

In fact, I have used different validators (like api validator, swagger editor) to validate the file I want to use, and they all say it's a valid file.

Swagger-codegen version

Online generator

Swagger declaration file content or url

https://www.zuora.com/developer/yaml/swagger.yaml

Command line used for generation

curl -X POST -H "content-type:application/json" -d '{"swaggerUrl":"https://www.zuora.com/developer/yaml/swagger.yaml"}' https://generator.swagger.io/api/gen/clients/python

Steps to reproduce

Run the following commands in terminal (I'm using macOS Monterey version 12.4):

curl -X POST -H "content-type:application/json" -d '{"swaggerUrl":"https://www.zuora.com/developer/yaml/swagger.yaml"}' https://generator.swagger.io/api/gen/clients/python

Related issues/PRs

Didn't find any

Suggest a fix/enhancement

Not sure if it's a bug or it's the problem on my end. I would really appreciate if you could add more description in the error message rather than just saying the file is invalid.

Start by reproducing the failure with the provided curl request against generator.swagger.io using the Zuora swagger.yaml URL, then inspect the online generator's validation path and its error handling. Done means the valid specification is accepted or the response identifies the actual validation problem instead of only reporting that it is invalid.