Drive API, PERMISSION_DENIED error

[erc_gong]

I am trying to upload files to a Shared Drive, and then update them on a regular basis. I use python, and the script can upload files without any issue. But it couldn't update/replace those files. I made another scrip to list files in the same Shared Drive folder and then delete them and I got the following error:

{"error":{"code":403,"message":"The request is missing a valid API key.","errors":[{"message":"The request is missing a valid API key.","domain":"global","reason":"forbidden"}],"status":"PERMISSION_DENIED"}}

I am using OAuth 2.0, that shouldn't need API key, right?

Am I missing any setting/permission on Google?

Thanks