The notifications API v2 client has an operation to update behavior group actions. In tests, I provided a behavior group id and a list of request body parameters as mandated by the spec. The associated test looks like this:

test('update behavior group actions', async () => {
  const params: NotificationResourceV2UpdateBehaviorGroupActionsParams = {
    behaviorGroupId: 'behaviorGroupId',
    requestBody: ['a', 'b', 'c'],
  };
  const resp = await client.notificationResourceV2UpdateBehaviorGroupActions(params);
  expect(resp.status).toBe(200);
}); 

When I set up mitmproxy to intercept the client request, the format was very different from what I expected to see. 

1. The behaviorGroupId rendered in the URL as "%5Bobject%20Object%5D", which suggest that the formatting of this input parameter isn't performed properly.
2. The request did not have a request body; this means that the "requestBody" input parameter was effectively ignored.

For reference, here is a screencap of the request data taken from mitmproxy: