Getting error "This employee is not authorized to make approvals"in "MakeDecision" method.



my use case has approval workflow as below

1. It is one level approval and has two approval steps.

a. first step is "BS": back to requester

b. second is "EX": external approval. External approval calls custom process and this custom process has "Make Decision" call at the end which sends the decision back to request. 

so here, it is able to execute the first step in process but throws error on second step which is Make Decision call. Someone please help in resolving this issue. Thanks in advance