Are you getting the below error message when attempting to run the Web Connector?
Message: "QBWC1012: "Authentication failed due to the following message: Response is not well formed XML"
This typically means that there is at least one blank line that's being added to the top of your site's output - and is also being included in responses to the Web Connector, causing it to fail.
In the rare cases we see this, it can be caused by a runaway/unintentional blank line after a PHP closing tag in custom code on your site.
Steps to Resolve
We recommend relaying this information to your web developer, as it It is usually simple for them to either review custom theme/plugin code on your site to remove blank lines after a PHP closing tag - and/or disable/enable plugins or themes temporarily to identify the culprit - so it's not present in your site response, and thus in our web service URL.
Temporarily disabling plugins / themes one by one until the blank line(s) in our web service URL dissapear - which helps locate the cause of these additional lines being added to the output of your site.
If your web developer has difficulty locating the code on your site causing this issue, we'd be happy to help take a closer look as a courtesy via support ticket in your account with us.