Data transform is used to set the pyExpanded flag for an expandable row in a repeat grid. The row does not expand at run time, unless the "Enable displaying details on multiple rows" option is checked.
Steps to Reproduce
Create a Grid Repeat Layout in a section.
Configure the layout. In Operations tab > Row operations > Display of details > select 'Expandable rows' . Check the option to "Enable displaying details on multiple rows".
Configure a custom Data Transform or an Activity on the Flow Action which is calling the particlaur section.
Set the pyExpanded flag to true (setting this flag programmatically in activity or data transform rule)
The row expands and sets this flag programmatically.
Without "Enable displaying details on multiple rows" being checked, system does not allow modifying row level properties from Activity or Data-Transform.
This is an expected behavior. To make sure, that the rows expands using pyExpanded check the correct page in the clipboard under pyWorkPage.