When a Blackbaud Online Express donation form is added to a Web page that does not meet security recommendation, a Security Warning may appear. This security warning may persist for up to three days after the issue is corrected.
If 72 hours have passed after correcting the issue, ensure that your website's Content Management System directs all page loads of the page with your form embedded on it through a secure connection. If a donor can still type "http" and load the page with the Online Express form on it, this error will continue to appear.
If the secure connection is in place, Contact Support and reference this article.