Hello Rameshwari,
It happens because of wrong API usage.
There is the modified task object in the onLightboxSave event handler: https://docs.dhtmlx.com/gantt/api__gantt_onlightboxsave_event.html
It overwrites all changes in the existing task object.
You try to modify the changes in the existing task object, so it is expected that it doesn’t work.
Instead, you can use the task object from the function.
Also, you don’t need the following lines:
The changes will be repainted and the task will be updated after you return true in the onLightboxSave event handler.
Here is the updated snippet where it works correctly: http://snippet.dhtmlx.com/5/6c6a88262
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