Firebase returns invalid-action-code, when verifying an email. Things to note: i made my own email logic/template; ie I manually generate the codes on firebase functions and dispatch them in the sent email.

The issue is, even though it returns "invalid-action-code", the user gets verified correctly. So it's a false positive. However I cannot differentiate from real-invalid-code cases.

    const auth = getAuth();
    let error = false;
    await applyActionCode(auth, actionCode)
        .catch(err => {
            error = {
                code: err.code,
                message: err.message
            }
        })