Using the DocumentOutputRequestPreview_MD can't preview, which step I miss?

Hi experts,
I want to preview the choose item at OWL, I want to use the DocumentOutputRequestPreview_MD, but I try it some times, it is failed.

https://answers.sap.com/questions/266792/how-can-using-the-documentoutputrequestpreview-md.html

Who can do me a favour?Thanks a lot.
Best Regards,
Benny