Here’s link to PART1 https://mps4hana.com/2025/08/21/internal-order-or-project-wbs-part1/

And now let’s look at High-level plan and activities for a scenario /situation : where we require migration steps from Legacy (SAP ECC) to New system (SAP S/4HANA) in which Client was using Internal Orders in ECC and going-forward Client used Project-WBS, instead of Internal Order.

This scenario is common in S/4HANA Greenfield or Selective Data Transition (SDT) projects, where companies move from using Internal Orders for cost tracking to using the Project System (PS) WBS structure in S/4HANA.

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🔹 Migration Steps: ECC (IO) → S/4HANA (PS-WBS)

1. Preparation Phase

• Identify scope: Which Internal Orders (open & historical) need to be migrated?
• Classify:
  • Active IOs → To be converted into WBS elements.
  • Closed IOs → Archived (no migration needed).
• Mapping:
  • IO Master Data (Responsible CCtr, Profit Center, Settlement Rules, Status) → WBS attributes.
  • IO Categories (Overhead, Investment, Accrual, etc.) → PS object type (Project Definition / WBS).
• Freeze new IO creation in ECC at cutover date.

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2. Master Data Migration

• Extract Internal Orders from ECC (SE16N / AUFK, COAS).
• Define Target WBS hierarchy in S/4HANA:
  • Create Project Definitions (CJ20N / LTMC / BAPI_PROJECT_MAINTAIN).
  • Create WBS elements mirroring IO structure.
• Map IO numbers to WBS codes (store mapping in conversion table for audit).

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3. Open Commitments Migration

• Extract open PRs/POs against IOs in ECC.
• In S/4HANA, recreate PR/PO referencing WBS.
• Ensure Purchase Orders reference new WBS element instead of IO.
  • Tools: LTMC for MM migration, or custom BAPI programs.

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4. Actual Costs Migration

• Historical Costs (Optional):
  • Extract historical postings (BKPF/BSEG + COEP).
  • Load into S/4HANA WBS via FI journal entries (BAPI_ACC_DOCUMENT_POST) with WBS reference.
• Open Balances (Mandatory):
  • Post migration journal entry: Dr Expense A/c (WBS) Cr Expense A/c (Technical clearing, IO reference)
  • This clears IO balances and assigns them to WBS.
• Repostings: If parallel systems run during cutover, use KB11N / BAPI_ACC_PRIMARY_COSTS_POST to repost open costs.

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5. Settlements / Capitalization (if relevant)

• If IOs were used for Asset Under Construction (AUC):
  • Run final settlement in ECC (KO88).
  • Migrate resulting AUC balances to WBS/Investment Projects in S/4HANA (via CJ88 in new system).

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6. Validation

• Compare balances:
  • ECC IO report → KOB1, S_ALR_87012993
  • S/4HANA WBS report → CJI3, S_ALR_87013558
  • Ensure totals match for costs, commitments, revenues.
• Reconcile with Trial Balance to ensure financial correctness.

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7. Closing Legacy IOs

• In ECC, mark IOs as:
  • CLSD (Closed)
  • DLFL (Deletion Flag)
  • Ensure no future postings.

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8. Post-Go-Live

• Redirect all derivations:
  • OKB9, substitution/validation rules → WBS instead of IO.
• Train business users to use PS reports instead of IO reports.
• Archive old IO data if required.

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🔹 High-Level Cutover Plan

Phase	Key Activities	Responsible
T-4 Weeks	Freeze new IO creation, mapping IO → WBS	Finance/CO
T-3 Weeks	Extract IO master data, create Projects/WBS	PS/IT
T-2 Weeks	Migrate commitments (PR/PO)	MM/Finance
T-1 Week	Dry run: Repost sample costs	Finance/IT
Cutover Weekend	Final cost transfer, final settlement, IO closure	Finance
T+1 Week	Validation & reconciliation	Finance/Business

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✅ Net effect: After cutover, all future postings go to WBS in S/4HANA, while IOs are frozen and only retained for historical reference in ECC.