You may have received an error message in Funnel advising you to disable your ad blocker:
When connecting ad accounts and Google Analytics views in Funnel, a new window is opened with the connection dialog. It's therefore important to ensure that your ad blocker is disabled or has whitelisted all Funnel domains.
Disabling your ad blocker
In order to disable your ad blocker, simply click on the extension and select "Pause AdBlock" or something similar depending on the extension you're using:
If using "AdBlock" you should notice that the icon in your browser changes to a green 'thumbs up' and the status is set to paused.
You should now be able to connect new sources to Funnel as expected.
Whitelisting Funnel domains
Whitelisting Funnel's domains allows you to keep the ad blocker running, but ignore all Funnel related pages. In order to whitelist Funnel domains you need to ensure that the following domains are whitelisted/set to "Don't run":
The first domain applies to the Funnel app whereas the second and third domain applies to the connector window. This means that you'll need to ensure all three domains are whitelisted so Funnel works as expected.
Last resort
If you're still receiving this error after following the steps above, we would suggest removing the ad blocker extension completely or try using another browser.