Facing issue while setting dynamic value in failedJobRetryTimeCycle

Hi,

I am implementing retry mechanism for each task separately, for that I am using the failedJobRetryTimeCycle. It is working if I provide the value directly. But it is not working if I configure $ variable.

Working code:
<serviceTask id="sid-FF86AA94-5636-4E15-B03A-B04900885AEE" name="Test Case" flowable:async="true" flowable:delegateExpression="${testTask}"><extensionElements><flowable:failedJobRetryTimeCycle>R5/PT3M</flowable:failedJobRetryTimeCycle></extensionElements></serviceTask>

Not working code:
<serviceTask id="sid-FF86AA94-5636-4E15-B03A-B04900885AEE" name="Test Case" flowable:async="true" flowable:delegateExpression="${testTask}"><extensionElements><flowable:failedJobRetryTimeCycle>${retryconfig}</flowable:failedJobRetryTimeCycle></extensionElements></serviceTask>

Dont understand why direct value “R5/PT3M” is working and dynamic value ${retryconfig} is not working.

Please help me on how to configure dynamic values in extension elements.

Thanks,
Kalyan