Approving the Submited Approval through Apex code

[Jerry]

I am Facing the problem when  i am Approving the Submited Approval  through Apex code 

and i am countered with this error pl help me out .

System.DmlException: Process failed. First exception on row 0; first error: INVALID_CROSS_REFERENCE_KEY, invalid cross reference id

public void Reject (){

update perform;
Approval.ProcessWorkitemRequest req2 = new Approval.ProcessWorkitemRequest();
req2.setComments('Rating are not up to the mark');
req2.setAction('Reject'); //This is the action that is approve in your case, you can set it to Reject also

req2.setNextApproverIds(new Id[] {UserInfo.getUserId()});
// Use the ID from the newly created item to specify the item to be worked

req2.setWorkitemId(perform.id);

// Submit the request for approval

Approval.ProcessResult result2 = Approval.process(req2);
System.assert(result2.isSuccess(), 'Result Status:'+result2.isSuccess());

System.assertEquals(
'Approved', result2.getInstanceStatus(),
'Instance Status'+result2.getInstanceStatus());

}

[Jerry · Accepted solution]

Approval.ProcessWorkitemRequest[] prWkItems = New Approval.ProcessWorkItemRequest[]{};
            //Reject the record
            ProcessInstance[] pi = [Select ID, Status, TargetObject.Name, 
                (SELECT Id, ActorId, ProcessInstanceId FROM Workitems),
                (SELECT Id, StepStatus, Comments FROM Steps) From ProcessInstance 
                Where TargetObjectID IN :tbuApprovals AND Status = 'Pending'];
            
      
            
            for(ProcessInstance instance : pi){
      
                for(ProcessInstanceWorkItem workItem : instance.WorkItems){
                  
                  
                    Approval.ProcessWorkitemRequest prWkItem = new Approval.ProcessWorkitemRequest();
                    
                    prWkItem.setWorkItemID(workItem.id);
                    prWkItem.setComments('Request Canceled by User: ' + userInfo.getName());
                    prWkItem.setAction('Reject');
                    prWkItems.add(prWkItem);
                  
                }
            }          
            
            if(!prWkItems.isEmpty()){
                shouldTriggerRun.stopFAR();
                Approval.ProcessResult[] appResult = Approval.process(prWkItems);
                shouldTriggerRun.allowFAR();
            }