Approval Workflows for Purchase Orders and Change Versions 
0-step approval workflow (WS14000075)
This workflow starts if, according to the start conditions, no approval is required. As a result, the purchase order (PO) is released or the changes to the purchase order change version (PO-CV) are transferred to the active document.
1-step approval workflow (WS14000089)
This workflow requires approval of the PO / PO-CV by the manager of the relevant purchasing organization. If the manager approves, the PO/ PO-CV is released; if he rejects, the PO/ PO-CV gets the status rejected, the workflow is terminated and the creator can reprocess the PO/ PO-CV and submit it for approval again.
The creator, the approver, and the reviewer can add further approvers/reviewers to the approval chain and also replace these:
Workflow user |
Add/replace approvers and/or reviewers |
|---|---|
Creator |
During approval at each stage of the approval chain (after the current stage) When creating the PO/ PO-CV (that is, before ordering) unrestricted at each stage |
Approver |
At each stage of the approval chain (after his own stage) |
Reviewer |
At each stage of the approval chain (after the current stage) |
You define the authorization for adding/removing approvers or reviewers in the processor assignment for workflow template WS14000089 in Customizing for SAP Supplier Relationship Management under 
SRM Server 
Cross-Application
Basic Settings Business Workflow Application-Controlled Workflow Technical Configuration Perform Task-Specific Customizing 
.
Features:
Approvers cannot change PO / PO-CVs that are already in the approval process.
If the manager rejects, the approval workflow is terminated and the PO / PO-CV gets the status rejected. This means that the creator can now delete or process the rejected PO / PO-CV and can order it again.
As long as the PO / PO-CV is in the approver's inbox, the creator can change it: Once the changes are saved, the current approval workflow is terminated and a new approval process is started.
Changes to the approval process (adding/removing of approvers/reviewers, adding of internal notes/attachments) do not lead to a restart of the workflow.
n-step approval workflow (WS14000145)
This workflow is intended for longer (more than 2-step) approval processes where it is necessary that the approver and the creator can both make changes to the PO / PO-CV during the approval process without the workflow being interrupted and having to be restarted.
The characteristics of n-step approval workflows are described in the following documents: