Magento – Magento 2.2 something went wrong with the subscription

The only place I can find that exact string is in Magento_Ui/view/base/web/js/grid/provider.js in the function onError(). It looks like anywhere in the admin a grid is being used, this component is initialized. I would start by looking at your xhr requests in the chrome inspector network tab and finding any responses that don't return a 200 code. If you can confirm that this ajax request is related to the action that gave you that alert message, you can go from there.

It's unable to send the email confirmation for whatever reason. You need to configure your server to allow php to send emails.