Cannot create interrupting timer event for a servie task

[cocoylq]

Here is a process copied from Camunda Doc online.

Now, I want to create the interrupting timer event on a service task. You can see it from the content circled in the red circle . I added a intermediate event from the left panel, and modified its type with “timer intermediate catch event” .Then I drugged it to the boundary of a task, however it shows a forbidden signal and the task turns red.

So, my question is How can I create the interrupting timer event for a task using camunder modeler.

I would appreciate any help in resolving this doubt.
Thank you in advance.

[cocoylq]

Hi, every one. I have solved the problem . I drugged the intermediate event directly from the left panel to the boundary of the task. That is ok.
I mean you need not to add the event to the diagram and then try to drug it to the boundary of a task.