Firebase denies permission after first time then works on second time - reactjs

Question

Firebase denies permission after the first time to push data to realtime database... but then works when I push data on the second time...
export const writeClass = async (
courseId,
topicName,
classIntro,
youtubeLinkId,
classNoteLink
) => {
const dbRef = ref(getDatabase());
try {
const totalClasses = await get(
child(dbRef, `Courses/${courseId}/totalClasses`)
);
var totalClassesNum = parseInt(totalClasses.val()) + 1;
console.log(totalClasses.val());
const msg = await update(
ref(db, `Courses/${courseId}/classes/${totalClassesNum}`),
{
classIntro: classIntro,
topicName: topicName,
youtubeLinkId: youtubeLinkId,
classNoteLink: classNoteLink,
}
)
.then(() => {
update(ref(db, `Courses/${courseId}`), {
totalClasses: totalClassesNum,
});
console.log("Section added");
return true;
})
.catch((error) => {
console.log(error.message);
// alert(error.message)
return error.message;
});
return msg;
} catch (error) {
// alert(error.message)
console.log(error);
}
};
The firebase rules :
".write" :
"root.child('specialUsers').child(auth.uid).child('is_admin').val()
=== true

Answer 1

Firebase automatically restores the signed-in user when the page reloads/app restarts, but this requires it to call the server (to check a.o. whether the account was disabled) and that may take some time.
This means that the first time your code runs the user may not be signed in yet, and you need to check for that in your code. It's a bit unclear exactly where in your code the problem occurs, but you'll want to wrap that in:
if (firebase.auth().currentUser !== null) {
...
}
Even better would be to react to when the user is signed in or out, which you can do as shown in the first snippet in the documentation on getting the currently signed in user:
import { getAuth, onAuthStateChanged } from "firebase/auth";
const auth = getAuth();
onAuthStateChanged(auth, (user) => {
if (user) {
// User is signed in, see docs for a list of available properties
// https://firebase.google.com/docs/reference/js/firebase.User
const uid = user.uid;
// ...
} else {
// User is signed out
// ...
}
});