What Permission Scopes required for Google Cloud Platform Channel API - customers.create - node.js

Question

Overview
I am getting an error insufficient permission scopes when running customers.create GCP Channel API, but I can't tell what extra permissions/scopes I need to grant my service account.
I have a node.js provisioning some GCP Resources, where one of the main goals is to automatically create a new Billing Subaccount in GCP.
The latest documenation for this suggests creating a customer, them creating entitlements from there. (A customer is passed into the "create entitlements" method).
Expected Results
Execution of the create customer method should have a successful out of a customer object.
Actual Results
When I implement the create customer I get an error:
UnhandledPromiseRejectionWarning: Error: 7 PERMISSION_DENIED: Request had insufficient authentication scopes.
at Object.callErrorFromStatus ...
My implementation
Authentication : service account credential file
I have a service account with an exported key/credential file I use to successfully authenticate other GCP API calls in my application such as projects.create() and projects.serviceAccounts.create() - so I am confident that my service account authentication is set up correctly as far as the node application goes.
Service account authentication in code:
const auth = new google.auth.GoogleAuth({
keyFile: 'MyServiceAccountKey.json',
scopes: [
'https://www.googleapis.com/auth/cloud-platform',
'https://www.googleapis.com/auth/apps.order',
'https://www.googleapis.com/auth/cloud-billing'
],
});
Service Account Permissions (Granted at folder level)
Permissions contained within the "Customer Billing Admin" Role:
Channel API Method Execution :
const {CloudChannelServiceClient} = require('#google-cloud/channel').v1;
async function CreateCustomer(options){
const channelClient = new CloudChannelServiceClient();
const authClient = await auth.getClient();
const request = {
parent : "accounts/XXXXX-XXXXX-MYACCOUNT",
customer : {
"name": "Customer Test 1",
},
}
const response = await channelClient.createCustomer(request);
console.log(response);
}
Resolution thoughts
Using the GCP APIs I've found that sometimes I just need to add additional permissions to my service account in the IAM page on the GPC console, and other time I needed to include more scopes in the authentication object in my code. This refercence for the accounts.customers.create says the required scope for this api is https://www.googleapis.com/auth/apps.order, which I have included in my code - so I am at a loss as to what permissions/scopes I am missing. From what I can tell, service account authorization should work with this API.