Match subcontract processing bills to the right quantity and operation

Why three-way matching breaks on subcontract processing invoices

In forging, metal fabrication, heat treatment, electroplating, and surface-coating plants, raw or semi-finished components are sent to external job-work processors under an outward material challan and returned days later with a processing service invoice. Standard ERP three-way matching (PO price × Goods Receipt quantity) fails routinely on subcontract bills because four different quantities exist on the same job-work lot:

1. Outward dispatched quantity/weight (Challan_Out): The gross weight or piece count shipped from your stores to the processor (for example, 200 rough forgings weighing 2,460.0 kg including forging flash and scale).
2. Gross returned quantity/weight (Gate_Receipt_In): The physical weight or piece count received back at your weighbridge after heat treatment and shot-blasting (for example, 198 forgings weighing 2,415.4 kg after scale loss, with 2 pieces missing or scrapped at the vendor).
3. Quality-accepted good quantity/weight (Accepted_Good_Qty): The net quantity that passes incoming hardness and crack inspection (M007) on the first pass (for example, 185 good forgings weighing 2,257.0 kg, while 13 pieces require re-tempering due to low hardness).
4. Re-processed or reworked quantity (Rework_Cycle_Qty): The 13 under-hardened pieces sent back for re-tempering—which the vendor sometimes bills a second time if AP does not link the rework challan to the original quality rejection.

Direct answer: To pay subcontract processors accurately without leaking margin or losing stock custody, your AP matching workflow must bind each subcontract purchase order line to an explicit Billing Basis Rule (Per_Accepted_Good_Piece, Per_Accepted_Net_Kg, or Per_Dispatched_Input_Kg_With_Cap), verify the physical challan mass balance (S02, M006), deduct vendor-caused rework cycles (M007), and route any abnormal material shortage or unapproved extra-operation surcharge to the Subcontract Buyer before posting the invoice (S18).

As documented in ERPNext subcontracting workflows, a subcontracting cycle tracks raw material transfers to the supplier warehouse separately from service receipts and material consumption. Meanwhile, Microsoft Dynamics 365 accounts payable invoice matching enforces price and quantity matching tolerances against product receipts. For Indian operations, CBIC Circular No. 38/12/2018-GST on job work procedures provides historical regulatory context on challan tracking and return timelines under GST; because tax circulars and filing rules (such as ITC-04 and e-waybill rules) are periodically amended, always verify current statutory GST compliance and tax-invoice/debit-note rules with your qualified tax advisor.

Subcontract Job-Work Invoice Reconciliation and Material-Balance Gate

Follow the workflow below, or open its complete text version.

Read the complete workflow as text

1. Receive Subcontractor Service Invoice + Return Challan Refe... → Reconcile Physical Material Balance: Dispatched vs Good + R...
2. Reconcile Physical Material Balance: Dispatched vs Good + R... → Hold Unreconciled Shortage Quantity & Escalate to Subcontra...
3. Hold Unreconciled Shortage Quantity & Escalate to Subcontra... → Look Up Contracted Billing Basis (Accepted Piece vs Accepte...
4. Look Up Contracted Billing Basis (Accepted Piece vs Accepte... → Filter Out Vendor-Responsible Rework Cycles & Unapproved Ex...
5. Filter Out Vendor-Responsible Rework Cycles & Unapproved Ex... → Compute Verified Payable Service Amount = Eligible Qty/Weig...
6. Compute Verified Payable Service Amount = Eligible Qty/Weig... → Approve & Post Undisputed AP Service Invoice
7. Approve & Post Undisputed AP Service Invoice → Split Invoice: Release Undisputed Portion / Hold Disputed D...

Worked example: heat-treatment and shot-blasting bill with dispatch-vs-accepted weight variance

The following scenario, challan numbers, forging weights, processing rates, and invoice lines are explicitly illustrative and use assumed values to demonstrate quantity/weight basis reconciliation and AP variance partitioning.

Suppose a closed-die forging plant dispatches Lot FG-LOT-908 consisting of 200 alloy-steel gear blanks (Part GB-450) to external processor HT-VEND-12 on Outward Job-Work Challan JWC-2026-1405 against Subcontract Purchase Order SPO-2026-312.

1. Contract terms on SPO-2026-312

• Operation 10 (OP-HT: Quench & Temper Heat Treatment): Contract rate = ₹18.00 per kg of quality-accepted net returned weight (Basis: Accepted_Net_Kg), with an allowed non-recoverable scale/oxidation loss allowance of up to 1.00% of dispatched weight.
• Operation 20 (OP-SB: Shot-Blasting): Contract rate = ₹12.00 per quality-accepted piece (Basis: Accepted_Good_Pieces).
• Pre-approved extra operation (OP-STR: Hydraulic Press Straightening on shafts exceeding runout): Authorised via written engineering/buyer amendment AMD-312-A on a maximum of 30 pieces at ₹25.00 per piece (₹750.00 ceiling).
• Rework & abnormal scrap policy: Re-tempering of pieces failing hardness spec (280–320 HBW) is at the subcontractor's expense (₹0.00 service charge). Irreparable vendor-scrapped pieces above 0 pieces are held for commercial replacement/debit review (M044, standard forging blank cost = ₹650.00 per piece).

2. Physical weight and piece reconciliation across Challan JWC-2026-1405

• Outward dispatch (JWC-2026-1405):
  • 200 pieces at 12.30 kg/piece gross weight = 2,460.0 kg dispatched.
• Inward return & incoming metallurgical inspection (GRN-JW-881 & INS-JW-409):
  • Accepted first-pass good pieces (Accepted_Good): 185 pieces at 12.20 kg/piece net post-scale weight = 2,257.0 kg.
  • Rejected for low hardness (Sent_For_Vendor_Rework): 13 pieces at 12.20 kg/piece = 158.6 kg (later re-tempered and accepted on Rework Challan JWC-2026-1405-R1, bringing total eventually accepted pieces to 185 + 13 = 198 pieces weighing 2,257.0 + 158.6 = 2,415.6 kg).
  • Cracked during improper quench at vendor (Vendor_Damaged_Scrap): 2 pieces returned as cracked scrap weighing 24.4 kg.
  • Physical scale / furnace oxidation weight loss (Process_Scale_Loss): 2,460.0 kg (dispatched) minus (2,257.0 kg + 158.6 kg + 24.4 kg) = 2,460.0 minus 2,440.0 = 20.0 kg (20.0 ÷ 2,460.0 = 0.813%, which is within the 1.00% scale allowance).
  • Piece count conservation check: 185 (first-pass good) + 13 (reworked good) + 2 (cracked vendor scrap) = 200 pieces dispatched.

3. Reconciling the subcontractor's submitted invoice (INV-HT-7741) against verified entitlement

When HT-VEND-12 submits Invoice INV-HT-7741 for ₹50,955.00 (before GST), AP runs the four-line reconciliation bridge:

Check every arithmetic component of the variance:

1. Line 1 (OP-HT weight variance breakdown):
   • Disallowed rework second-pass billing: 158.6 kg × ₹18.00/kg = ₹2,854.80.
   • Disallowed billing on 20.0 kg furnace scale loss + 24.4 kg cracked scrap (44.4 kg total non-good weight): 44.4 kg × ₹18.00/kg = ₹799.20.
   • Exact Line 1 check: ₹43,480.80 (verified) + ₹2,854.80 (rework) + ₹799.20 (scale + cracked) + ₹0.20 (vendor rounding) = ₹47,135.00.
2. Total service invoice check: ₹43,480.80 + ₹2,376.00 + ₹750.00 + ₹0.00 = ₹46,606.80 verified payable vs ₹50,955.00 billed (₹50,955.00 minus ₹46,606.80 = ₹4,348.20 overcharge).
3. Separate commercial material claim for the 2 cracked forgings (CLM-JW-1405):
   • In addition to blocking the ₹4,348.20 service overcharge, the 2 cracked gear blanks (2 × ₹650.00 = ₹1,300.00 raw forging value) remain open on Material Exception Record MEX-1405.
   • Under the approval boundary rule (M044), AP does not blindly auto-deduct ₹1,300.00 from the ₹46,606.80 service bill without commercial sign-off; instead, AP holds payment of the disputed portion or links the buyer-approved debit note (DN-2026-091 = ₹1,300.00) once Supplier Quality and the Subcontract Buyer confirm vendor quench liability.

Governance matrix: who owns each subcontract exception

Acceptance criteria for subcontract invoice reconciliation

1. Dual-unit challan preservation (TEST-M066-01): Every subcontract receipt records both piece count and measured weight alongside Accepted_Good, Rework_Required, Returned_Scrap, and Process_Loss buckets so Dispatched = Good + Rework + Scrap + Loss.
2. Contract basis enforcement (TEST-M066-02): When a subcontract PO specifies Basis = Accepted_Net_Kg or Accepted_Good_Pieces, the AP matching engine computes payable entitlement from inspected good receipts rather than raw outward dispatch weight.
3. Rework double-billing block (TEST-M066-03): Return receipts linked to a vendor-fault rework challan increment physical stock custody recovery without generating a second payable service accrual.
4. Separated service variance vs material loss liability (TEST-M066-04): Disputed material scrap liability (M044) is tracked as an explicit commercial claim record rather than silently altering the unit service rate or closing an unbalanced material challan.

Synthesis and next actions

Matching subcontract processing bills requires connecting three records that most plants keep in separate silos: the contracted rate basis on the PO, the physical weight/piece balance on the challan, and the incoming quality disposition on the return lot.

1. Add an explicit Billing_Basis_Code to every subcontract PO line: Specify on the purchase order whether the processor is paid per Dispatched_Input_Kg, Returned_Net_Kg, or Accepted_Good_Piece, along with the maximum allowable process-loss percentage (S02, S18).
2. Record both pieces and weight at outward dispatch, inward gate receipt, and quality acceptance: Ensure weighbridge and inspection screens capture net post-process weight on Accepted_Good lots separately from rejected or scrapped returns (M006, M007).
3. Tag rework return challans to the originating NCR: Configure the ERP so parts sent back to the vendor to rectify a processing defect are tracked for material custody without creating a duplicate billable service receipt.
4. Reconcile open challan ageing and tax timelines monthly: Review open job-work challans with Stores, Procurement, and Finance each month to verify physical stock reconciliation and compliance with current GST job-work return rules (S21).