firebase sendEmailVerification does not give error on non exisent email address

I'm developing an authentication system for my React app with Firebase Auth. When the user signs up, firebase auth registers the user (createUserWithEmailAndPassword) and returns a promise with auth.uid and auth.emailVerified set to "false". This is fine.

I then use sendEmailVerification() method so the email address can be verified. I've tested the code and it works ok for a "valid" and "existing" email address. "catch" does give error for duplicate email address as expected. The problem is, it does not send the NON-EXISTING email (which I suppose is the correct bahaviour) but its should then give an error (so I can display to the user) which it does not.

Can someone explain why I'm not getting error for NON EXISTENT email address?

export const unpSignUp = (newUser) => {
    console.log("newUser", newUser);
    return (dispatch, getState, { getFirebase, getFirestore }) => {
        const firebase = getFirebase();
        const firestore = getFirestore();
        firebase.auth().createUserWithEmailAndPassword(
        newUser.unp_a05_email,
        newUser.unp_a10_password
        )
        .then((response) => {
        return firestore
            .collection("unps")
            .doc(response.user.uid)
            .set({
                unp_a02_surname: newUser.unp_a02_surname,
                unp_a03_name: newUser.unp_a03_name,
                unp_a06_verify_email_sent_datetime: null,
                unp_a07_email_verified_on_datetime: null,
                unp_a18_acc_created_on_datetime: moment().format("YYYY MM DD HH:mm:ss"),
            });
        })
            .then((response) => {
            console.log("SIGNUP SUCCESS ", response);
            // user has been signed up, next step is to send verification email
            dispatch({ type: SIGNUP_SUCCESS })
        })
        .then(() => {
            // user has been signed up, next step is to send verification email
            console.log('send email adr verification')
            return firebase.auth().currentUser.sendEmailVerification()
        })
        .then( (response) => {
            console.log("Verification email sent", response);
            const user = firebase.auth().currentUser
            console.log('current user', user)
            const unp = firestore.collection("unps").doc(user.uid);
            return unp.update({
            unp_a06_verify_email_sent_datetime: moment().format("YYYY MM DD HH:mm:ss"),
            })
        })
        .then( () => {
            console.log(`unp_a06_verify_email_sent_datetime update to ${moment().format("YYYY MM DD HH:mm:ss")} `)
        })
        .catch((error) => {
            console.log("SIGNUP ERROR", error);
            console.log("SIGNUP ERROR CODE", error.code);
            console.log("SIGNUP ERROR MESAGE", error.message);
            dispatch({ type: SIGNUP_ERROR, error });
        });
    };
};