gmail.users.watch | error sending test message to Cloud PubSub projects/tms-erp-afourtech-assets/topics/gmail-watcher : User not authorized to perform this action.

I want to implement watch for new mails in INBOX for a Google Workspace email ID.

Already Verified Pointers:

1. I've made sure that client_id from service.json file has domain wide delegated authorisation for the scope being used.
2. I've also made sure that service account has Publisher access.
3. I've also made sure that client_email has Publisher access from the Pub/Sub Followed this solution

Still getting

{
      message: 'Error sending test message to Cloud PubSub projects/<PROJECT_ID>/topics/gmail-watcher : User not authorized to perform this action.',
      domain: 'global',
      reason: 'forbidden'
    }

Code:

import { google, Auth } from 'googleapis';
import { resolve } from 'path';

const serviceAccountPath = resolve('./service.json')
const scopes = [
    'https://www.googleapis.com/auth/gmail.metadata'
]
const emailToBeDelegated = 'email.id@domain.com'

class GoogleAuth {
    public auth;
    constructor(serviceAccountPath: string, scopes: string[], emailToBeDelegated: string){
        this.auth = this.getAuth(serviceAccountPath, scopes, emailToBeDelegated);
    }
    public async getAuthorizedJWT () {
        await this.auth.authorize();
        return this.auth;
      };
    private getAuth = (serviceAccountPath: string, scopes: string[], emailToBeDelegated: string): Auth.JWT => {
        return new Auth.JWT({
            keyFile: serviceAccountPath,
          scopes,
          subject: emailToBeDelegated
        });
      };
}

class GMailService extends GoogleAuth {
    constructor(serviceAccountPath: string, scopes: string[], emailToBeDelegated: string){
        super(serviceAccountPath, scopes, emailToBeDelegated);
    }

    watch = async () => {
        const auth = await this.getAuthorizedJWT();
        return google.gmail({ version: 'v1' }).users.watch({auth,
            userId: 'me',
            requestBody: {
                topicName: 'projects/<PROJECT_ID>/topics/gmail-watcher',
                labelIds: ['INBOX']
            }
        })
    }
}


(async () => {
    const gMailService = new GMailService(serviceAccountPath, scopes, emailToBeDelegated);
    console.log(await gMailService.watch());
})();

Beginne mit der im Issue gezeigten Methode GMailService.watch sowie den Methoden GoogleAuth.getAuth/getAuthorizedJWT. Reproduziere die users.watch-Anfrage mit dem angegebenen Gmail-Scope und Pub/Sub-Topic und ermittle anschließend, welche Autorisierungsgrenze sie ablehnt; abgeschlossen ist die Aufgabe, wenn eine bestätigte Ursache und eine reproduzierbare Lösung identifiziert wurden, da keine Repository-Datei oder kein Test genannt ist.