hi @saurabh vakil
already po fiori application working with backend system
gone through document link , as per this
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If you run on SAP NetWeaver lower than 7.4, assign the back-end system aliases for the Task Processing Service (/IWPGW/TASKPROCESSING Version 2) in Customizing for SAP NetWeaverunder 
Gateway
OData Channel Development with IW_BEPRegistrationAssign SAP System Aliases to OData Service
changed system aliases to backend, but its confusing...
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define task name and decision on backend
and gateway
anything wrong?
still 0