Can't operate an element in an popup dialog window

Katalon version: V5.9.1

Click an link, then popup an dialog window. then operate an element in this popup dialog window, report “Cannot find elements when the XPath expression is null.”
Before operate this element, I have try following switch method:
Switch to Window Url, Switch to Window Index, Switch to Window Index,
Those both didn’t work.
Script is like following.

log is like following.

Popup dialog window is like follwing

Object definition is following