Start by navigating to this page to begin the configuration. If your Slack user has the right privileges, you will be able to continue with this set up by clicking the "Add configuration" button (if you have not installed an Email app before you will instead be asked to "Install" it first):

Next, choose a Slack channel that the emails should be sent to. I named mine #connection-errors:

Now, Slack will generate an email address that the automatic notification emails should be sent to in order to appear in Slack. Select and copy this address:

Go to Configuration > Notifications in Funnel and set up a new notification (if you already have one set up, click "Edit notification" instead):

Enter the email address that Slack generated for you. 

Choose what time you want the notification to be sent, how often it should be sent and whether you want a notification even if there are no errors to just tells you that all is well. Hit the "Save" button when you are done and you are ready to test your shiny new notification!

Lastly, hit the "Run now" button to prompt a new notification email to be sent:

In your Slack channel that you chose in Step 1, you should see a new post shortly. It should look something like this:

If you click the "Reconnect ad accounts" link you will be taken straight to the Configuration > Ad accounts tab in Funnel. Happy reconnecting!

Note: Slack's own general step-by-step guide to setting this up can be found here.