To correct this error perform the following steps:
1. Navigate to Lists > Marketing > Marketing Templates.
2. Edit the Marketing Template.
3. In the HTML code locate the URL which normally starts with www (e.g. www.mywebsite.com).
4. Add http:// to the URL instead of just www (e.g. http://www.mywebsite.com).
5. Check the
6. Click Save.
7. Check email client for the email preview to verify that link works.
Note: This is just one of the many possible causes of 404 errors. If using the Publishable Form URL of a custom record, for example, make sure that permission settings were configured correctly for external users to access the form.