GET list of groups from cloudidentity.googleapis.com returns INVALID_ARGUMENT error

The end goal is to get a list of a user's groups after OAuth Authentication is completed using the supplied access token.

I'm currently having difficulty retrieving a list of groups from the Cloud Identity API after OAuth is completed.

Cloud Identity - Method: groups.list Documentation

Steps:

• Go to OAuth Playground
• Enter your own scope at the bottom of the list using "https://www.googleapis.com/auth/cloud-identity.groups.readonly"
• Click "Authorize APIs" button
• Choose the google account to use
• Allow the "Cloud Identity Groups"
• Click "Exchange authorization code for tokens" button
• Optionally "Auto-refresh the token before it expires."
• Click "List possible operations" Select "List Groups" - This populates the request URI. Click "Send the request"

GET /v1/groups HTTP/1.1
Host: cloudidentity.googleapis.com
Content-length: 0
Authorization: Bearer [TOKEN]

HTTP/1.1 400 Bad Request
Content-length: 127
X-xss-protection: 0
X-content-type-options: nosniff
Transfer-encoding: chunked
Vary: Origin, X-Origin, Referer
Server: ESF
-content-encoding: gzip
Cache-control: private
Date: Fri, 08 Nov 2019 16:12:32 GMT
X-frame-options: SAMEORIGIN
Alt-svc: quic=":443"; ma=2592000; v="46,43",h3-Q050=":443"; ma=2592000,h3-Q049=":443"; ma=2592000,h3-Q048=":443"; ma=2592000,h3-Q046=":443"; ma=2592000,h3-Q043=":443"; ma=2592000
Content-type: application/json; charset=UTF-8
{
  "error": {
    "status": "INVALID_ARGUMENT", 
    "message": "Request contains an invalid argument.", 
    "code": 400
  }
}

I've only ever been able to get invalid arguments with a status of INVALID_ARGUMENT. I've tried providing an API key from my own project, adding the parent parameter as required by the documentation.

Can someone please help with a valid request?

I have tried to get this working using the OAuth 2.0 Playground, the 'Try this API' functionality through the documentation and locally using a variety of options, I feel like I'm missing something simple.

Currently, the Cloud Identity groups API only provides access to Identity Mapped Groups, which makes it only relevant in the context of Cloud Search.

To access "regular" groups, use the Directory API.