I am using default Magento2.2.4. The subscription is working correctly. But when I am entering an email again, it is not showing any error. So if I enter email@example.com then I am getting subscribed in the list in admin. Which is correct. But if I enter the same email a second time, I am still getting success message, but ideally there should be a message that you are already subscribed.
Can someone help on how to fix this?