All firebase projects returning 'Missing or insufficient permissions'

Despite having changed my rules to the below, I am getting FirebaseError: Missing or insufficient permissions. Are there any other reasons firestore would return this error?

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {

    match /{document=**} {
      allow read, write;
    }
  }
}

Oddly, having checked other projects also live, I’m getting this error in ALL firebase projects, even ones I haven’t changed. I haven’t reached any quota limits and there’s nothing out of the ordinary in the firebase console. I have also tried accessing from a VPN to change my IP to no avail.