SAP_WAPI_DECISION_COMPLETE : 'No administrator found for the task'

Using FM SAP_WAPI_DECISION_COMPLETE to complete decision in inbound mail processing

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It is not completing the decision when it gets executed while inbound mail processing and returns 'No administrator found for the task' but when I execute the function module and pass the same values then decision is complete.

I tried :

1. SWU_OBUF

2. SO01--> settings --> workflow settings-->refresh organization environment