I can't send the messages

[ReaperBUL]

trafficstars

[JB-Dev]

Just replace the rules in your firestore with

service cloud.firestore {
  match /databases/{database}/documents {
    match /{document=**} {
      allow read, write;
    }
  }
}

[bharathmsd7]

Change the Firestore rules to

allow read, write: if true;

[darrylleung]

This change is absolutely necessary in the Firestore Rules tab. Not sure if this is something well known among Firebase users, but for new learners this information is not obvious.