Sometimes you have to search for an external account using very specific information, so try  finding your account using different variations of the name or link.
For example, search by the URL that displays when you log in directly to that external account: https://www.mycardstatement.com/#/
MX may again return the error above, so, try removing the extension after the “.com”: https://www.mycardstatement.com
If the connection is still not found, open a Zendesk ticket describing the issue.