DOR payload attribute to prohibit self approval by user

Hi,

We have a requirement for DOR to prohibit users from approving their own transactions.

Person for whom the transaction is performed,
if that person is in the approvers list then it should skip that person as approver and route to next approver.

Also, that person is not a task owner or creator here.

We have used AOR in approval rule and tried with below expression and it's not working.

task:task/task:payload/ns9:getRepresentativeListResponse/ns9:result/ns19:Username

Thanks,

Haripriya