Can't add documents and collections to Cloud Firestore to trigger Translate Text extension

Question

I tried to use Firebase Translate Text Extension to translate a text in my chat app project with Javascript. To do that, I have to add the target text into “document” at the Cloud Firestore (Add data to Cloud Firestore), but had the error:

"Uncaught (in promise) FirebaseError: Missing or insufficient permissions."

const docRef = await db.collection('translations').add({
    input: document.getElementsByTagName("body")[0].innerHTML,
    created: firebase.firestore.Timestamp.now()
});
console.log(docRef);

✔︎ Firebase rules are default.
✔︎ Firebase Deploy completed successfully
✔︎ Firebase Realtime Database works correctly
× Can't add document to Firestore Database data

I just followed this GitHub sample code.
Please someone help me out.
Thank you very much in your advance.

Firestore Rules

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /{document=**} {
      allow read, write: if false; //changed to "true" and it works
   }
  }
}