I am fixing an error message which occurred, but it also used to work before. I am sending FCM notification with multiple tokens and am getting the following error

0|api      | 2020-2-11 13:26:26   [ExceptionsHandler] Exactly one of topic, token or condition is required

0|api      |  +542752ms

0|api      | Error: Exactly one of topic, token or condition is required

0|api      |     at FirebaseMessagingError.FirebaseError [as constructor] (/var/www/tokee-api-new/node_modules/firebase-admin/lib/utils/error.js:42:28)

0|api      |     at FirebaseMessagingError.PrefixedFirebaseError [as constructor] (/var/www/tokee-api-new/node_modules/firebase-admin/lib/utils/error.js:88:28)

0|api      |     at new FirebaseMessagingError (/var/www/tokee-api-new/node_modules/firebase-admin/lib/utils/error.js:254:16)        0|api      |     at Object.validateMessage (/var/www/tokee-api-new/node_modules/firebase-admin/lib/messaging/messaging-types.js:46:15)

0|api      |     at /var/www/tokee-api-new/node_modules/firebase-admin/lib/messaging/messaging.js:265:31

0|api      |     at Array.map (<anonymous>)

0|api      |     at Messaging.sendAll (/var/www/tokee-api-new/node_modules/firebase-admin/lib/messaging/messaging.js:264:29)

0|api      |     at Messaging.sendMulticast (/var/www/tokee-api-new/node_modules/firebase-admin/lib/messaging/messaging.js:313:21)   0|api      |     at userChunks.forEach.userChunk (/var/www/tokee-api-new/src/modules/common/firebase/firebase.service.ts:154:42)     0|api      |     at Array.forEach (<anonymous>)

0|api      |     at FCMService.<anonymous> (/var/www/tokee-api-new/src/modules/common/firebase/firebase.service.ts:142:16)

0|api      |     at Generator.next (<anonymous>)

0|api      |     at /var/www/tokee-api-new/dist/src/modules/common/firebase/firebase.service.js:13:71

0|api      |     at new Promise (<anonymous>)

0|api      |     at __awaiter (/var/www/tokee-api-new/dist/src/modules/common/firebase/firebase.service.js:9:12)

0|api      |     at FCMService.sendToMany (/var/www/tokee-api-new/dist/src/modules/common/firebase/firebase.service.js:123:16)       0|api      |     at AdminNotificationController.<anonymous> (/var/www/tokee-api-new/src/modules/notification/admin-notification.controller.ts:65:42)

0|api      |     at Generator.next (<anonymous>)

0|api      |     at fulfilled (/var/www/tokee-api-new/dist/src/modules/notification/admin-notification.controller.js:16:58)

0|api      |     at <anonymous> 

The code producing the error:

async sendToMany(users: User[], notification: VSendNotification, title = 'Title', lowPriority = false) {

    // We split emails into arrays of max. 100 size because of the limitation with FCM

    const userChunks = _.chunk(users, 100);

    const promises = [];

    userChunks.forEach(userChunk => {

      const msg: admin.messaging.MulticastMessage = {

        notification: {

          title,

          body: notification.body

        },

        tokens: userChunk.map(user => user.firebaseToken),

        android: {

          priority: lowPriority ? 'normal' : 'high'

        }

      };

      promises.push(this.app.messaging().sendMulticast(msg));

    });

    const result = await Promise.all(promises);

    let accepted = 0;

    let rejected = 0;

    result.forEach(response => {

      accepted += response.successCount;

      rejected += response.failureCount;

    });



    return { accepted, rejected, notification };

  }

}

Thoughts on what could be wrong?