Error 709 : ContentId is not valid for the specified landing page content

[Neeraj_Bezalwar]

Hi,
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?

[Kenny_Elkington]

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.