Firebase FCM sendAll() private key error: error:0909006C:PEM routines:get_name:no start line

This error message based on its frequent appearance in SO seems to be a general response to a number of errors. I am trying to do a FCM sendAll(...) from a Nestjs microservice backend. I initalized the firebase in main.ts like so:

.......
......
 const app = await NestFactory.createMicroservice<MicroserviceOptions>(
    AppModule,
    {
     transport: Transport.TCP,
     options,
    }
  );
  const configService: ConfigService = app.get(ConfigService);
 
  const adminConfig: ServiceAccount = {
    "projectId": configService.get<string>('FIREBASE_PROJECT_ID'),
    "privateKey": configService.get<string>('FIREBASE_PRIVATE_KEY')
                               .replace(/\\n/g, '\n'),
    "clientEmail": configService.get<string>('FIREBASE_CLIENT_EMAIL'),
   };
    
  firebase.initializeApp({
      credential: firebase.credential.cert(adminConfig),
     });
  
  await app.listen();  
 
}
bootstrap();

My .ENV is like so:

 FIREBASE_PRIVATE_KEY    = "-----BEGIN PRIVATE KEY-----\nMI...\n-----END PRIVATE KEY-----\n",
  FIREBASE_CLIENT_EMAIL   = 'abc@my.com',
  FIREBASE_PROJECT_ID     = 'xxx-genysis'

apparently firebase was initialized and the credentials were ok. I do get an error if I substitute invalid credentials.

However, when I tried to execute the sendAll(...) in my notification.service.ts like so:

  import * as firebase from 'firebase-admin';
......
.....
async  sendNotifications(data) {
const messages = await this.getMessages(data.tokens,data.message,data.title);

    const promises = [];
    for (let i = 0; i + 10 <= messages.length; i += 10) {
        const batch = messages.slice(i, i + 10);
        promises.push(firebase.messaging().sendAll(batch));
    }
    await Promise.all(promises);
    
}

I am getting the following error:

error:0909006C:PEM routines:get_name:no start line
Error: error:0909006C:PEM routines:get_name:no start line
    at Sign.sign (node:internal/crypto/sig:131:29)
    at Object.sign (/Applications/GenysisBuild/GenysisNest/genysis-notifications/node_modules/jsonwebtoken/node_modules/jwa/index.js:152:45)
    at Object.jwsSign [as sign] (/Applications/GenysisBuild/GenysisNest/genysis-notifications/node_modules/jsonwebtoken/node_modules/jws/lib/sign-stream.js:32:24)
    at Object.module.exports [as sign] (/Applications/GenysisBuild/GenysisNest/genysis-notifications/node_modules/jsonwebtoken/sign.js:204:16)
    at ServiceAccountCredential.createAuthJwt_ (/Applications/GenysisBuild/GenysisNest/genysis-notifications/node_modules/firebase-admin/lib/app/credential-internal.js:105:20)
    at ServiceAccountCredential.getAccessToken (/Applications/GenysisBuild/GenysisNest/genysis-notifications/node_modules/firebase-admin/lib/app/credential-internal.js:77:28)
    at FirebaseAppInternals.refreshToken (/Applications/GenysisBuild/GenysisNest/genysis-notifications/node_modules/firebase-admin/lib/app/firebase-app.js:45:49)
    at FirebaseAppInternals.getToken (/Applications/GenysisBuild/GenysisNest/genysis-notifications/node_modules/firebase-admin/lib/app/firebase-app.js:37:25)
    at AuthorizedHttpClient.getToken (/Applications/GenysisBuild/GenysisNest/genysis-notifications/node_modules/firebase-admin/lib/utils/api-request.js:612:34)
    at AuthorizedHttpClient.send (/Applications/GenysisBuild/GenysisNest/genysis-notifications/node_modules/firebase-admin/lib/utils/api-request.js:600:21)

based on the responses to the error messages it would appears I have a bad private_key but this can't be the case since the same private key was used to initialize firebase. Can anyone shed some light on what's going on here?

EDIT: A try/catch error around the sendAll() result in the following error:

{"library":"PEM routines","function":"get_name","reason":"no start line","code":"ERR_OSSL_PEM_NO_START_LINE"}