I am trying to update a rich text content section of a Landing page with element like - <div id="heading" mktoName="Heading" class=" col-55 mktoText "> by REST API.
It throws 709: business rule violation.
If a change the css class to class=" mktoText " then the POST operation works. col-55 is a custom class created by the user, which can't be ignored.
How can I fix this error?
One thing you might try is trimming the trailing space at the end of your class list, that might be causing an issue, though that would still be a bug in my opinion.
If that doesn't work, I'd file a support case so that they can triage this, including your API request and response. It's not the correct behavior to reject a request if it includes multiple classes.