PO matching is the accounts payable control that compares an invoice to its approved purchase order before payment, to confirm the supplier, the amount, and the coding all agree. For outside counsel, the invoice is reviewed and approved in the ELM first, then sent to AP, where it is matched against a PO raised for that firm or matter. Law firm invoices bill hours against open-ended work, so the PO setup that suits a laptop order rarely suits a litigation matter. Get the structure right and legal invoices clear AP on the first pass. Copy the goods model unchanged and AP spends every month chasing exceptions on invoices legal already approved.
What is PO matching for legal invoices?
PO matching for legal invoices is the check AP runs to confirm that an ELM-approved law firm invoice belongs to an open purchase order for the same firm, with enough remaining balance to cover it. The PO represents the committed spend. The invoice draws it down.
For legal spend, the substance of the review happens before the match. Billing guideline checks, rate validation, and reviewer adjustments all take place in the ELM, so the invoice that reaches AP is already the approved net amount. The match confirms that this approved amount fits inside a commitment finance has authorized. That division keeps the two teams from reviewing the same invoice twice.
What is the difference between two-way and three-way matching for legal spend?
Two-way matching compares the invoice to the PO, while three-way matching adds a receipt confirming the goods or services were delivered.
- Two-way match. The invoice is checked against the PO’s supplier, balance, and coding. This is the most common setup for legal spend because there is no physical delivery to record.
- Three-way match. A service receipt confirms the work was accepted. For legal invoices, the ELM’s final approval acts as that receipt, and the integration can create it automatically when the invoice is approved.
- Four-way match. An inspection or quality record is added. This belongs to manufacturing and almost never applies to outside counsel.
If finance insists on three-way matching, generate the receipt from the ELM approval. Asking an in-house lawyer to log a separate receipt in the ERP adds a step nobody remembers to do, and invoices sit unpaid.
Which purchase order structures work for outside counsel?
Three purchase order structures work for outside counsel, and the right choice depends on how many firms you use and how closely finance tracks commitments.
- Blanket PO per firm per year. One PO covers all work a firm performs in a fiscal year. It is simple to maintain and suits departments with 10 to 40 active firms.
- PO per matter. Each significant matter gets its own PO, often above a threshold such as $50,000 in expected spend. Finance gets tight commitment tracking, and someone has to raise and close far more POs.
- PO per budget phase. Large litigation or deal matters get one PO line per phase, such as discovery or trial. This mirrors the matter budget closely and takes the most effort to maintain.
Most departments mix the first two, with blanket POs for routine work and matter POs for the handful of large matters. Whatever you pick, put the PO number on the matter or firm record in the ELM so every invoice carries it automatically.
Where should purchase order matching happen, in the ELM or in AP?
Purchase order matching should happen in AP as the final control, with a lighter pre-check in the ELM so failures surface while the invoice is still with legal.
- ELM pre-check. Before the invoice leaves the ELM, the integration confirms the PO exists, is open, belongs to the same firm, and has enough balance. Failures stay with legal operations, who can fix them quickly.
- AP final match. The ERP or AP platform runs its full matching rules and posts the invoice. With the pre-check in place, this step rarely fails.
- Balance sync. The pre-check needs a current view of PO balances, usually synced from the ERP every few hours.
The design of that connection follows the wider rule that every field in an ELM finance integration needs exactly one owning system, and here the ERP owns the PO.
What should a legal invoice be matched against on the PO?
A legal invoice should be matched against five elements of the PO, and all five must agree before it posts.
- Supplier. The invoice’s vendor is the same supplier the PO was raised for, including the correct remit-to site.
- Status. The PO is open and approved, with an end date that covers the invoice date.
- Remaining balance. The PO has enough uncommitted balance to cover the approved invoice amount.
- Currency and entity. The invoice currency and the legal entity being charged match the PO.
- Coding. The GL account and cost center on the invoice are allowed on that PO line.
Notice what is missing. Hourly rates, timekeepers, and task codes are checked in the ELM against billing guidelines that have been turned into enforceable rules. Repeating those checks at the PO level adds nothing and creates false exceptions.
How should tolerances work when matching legal invoices to POs?
Tolerances for matching legal invoices to POs should allow small overruns on balance and allow none on supplier or entity.
- Balance tolerance. Allow an invoice to exceed the remaining PO balance by a small amount, such as 5 percent or $1,000, whichever is lower. AP then flags the PO for a top-up without holding the invoice.
- Currency rounding. Allow a few cents of difference on converted amounts so exchange rate rounding never blocks a payment.
- Zero tolerance. Supplier, legal entity, and PO status must match exactly. A mismatch here usually signals a setup error or a misdirected invoice.
Review tolerance hits monthly. If the same PO trips the balance tolerance three months running, the PO was sized too small and should be increased.
What happens when a legal invoice fails the PO match?
When a legal invoice fails the PO match, it should land in a named exception queue with a readable reason and a clear owner.
- Insufficient balance. Finance or the matter owner approves a PO increase, typically within two to three business days, and the invoice is released.
- Closed or expired PO. The fiscal year rolled over or the matter closed. A new PO is raised and the invoice is re-pointed to it.
- Supplier mismatch. The firm billed under a different vendor record. Finance corrects the vendor ID mapping before the invoice is resent.
Tell the firm when an invoice is held and why. Most payment complaints from law firms come from silence. Clear exception routing is a large part of a smooth go-live, and hypercare defect triage gives each issue a severity and an owner the same day.
How do you measure PO matching performance for legal spend?
You measure PO matching performance for legal spend with three numbers: first-time match rate, exception rate, and time to clear exceptions. First-time match rate is the share of PO-backed legal invoices that post without manual handling. Exception rate is the share that needs someone to intervene. Clearance time is how many business days an exception sits before release.
The broader AP benchmark is high. Coupa’s 2024 Total Spend Management Benchmark Report found that top-quartile Coupa customers match 97 percent of invoices to POs and receipts without exception handling. Average teams sit lower, and a 2026 survey of nearly 200 AP and finance leaders found the average invoice exception rate is 19.9 percent. Legal invoices arrive already approved, so with a pre-check in place they can reach a similar level. Report these three numbers monthly alongside your other legal department KPIs, and set a clearance target of five business days or fewer.
How do you keep PO balances in step with matter budgets?
You keep PO balances in step with matter budgets by treating the matter budget as the source and the PO as the commitment that follows it. When a matter budget increases, the PO increase request should be raised from the ELM at the same time, so finance sees both together. When a matter closes, keep its PO open until the trailing invoice window ends, then close it within 30 days so the remaining balance is released.
Accruals sit between the two. Work billed late still needs to be estimated at month-end, and eBilling accrual configuration controls how unbilled legal work reaches the general ledger. A quarterly review comparing open PO balances to remaining matter budgets catches the drift before year-end, when most closed-PO exceptions happen.
Conclusion
PO matching works for legal invoices when the ELM handles the review and AP handles the commitment check. Choose a PO structure that fits how your department uses firms, pre-check every invoice before it leaves the ELM, set sensible tolerances, and give exceptions a named owner. Legal invoices will then post on the first pass, and finance keeps the spend control it asked for.
How Basla can help
Basla provides delivery teams for enterprise legal management and eBilling software implementation, covering legal technology consulting, PO and matter data design, integration specifications for AP, validation and exception workflow configuration, testing with finance, documentation, and hypercare after go-live. Basla teams have delivered matter management and eBilling programs across more than 10 global jurisdictions, and when timelines compress, Basla has doubled delivery team capacity to keep a program on schedule.
Frequently asked questions
What is PO matching for legal invoices?
PO matching for legal invoices is the AP check that confirms an approved law firm invoice belongs to an open purchase order for the same firm, with enough balance to cover it. Rates and billing guideline compliance are reviewed earlier in the ELM.
Do legal invoices need three-way matching?
Legal invoices rarely need true three-way matching because there is no physical delivery to receive. Where finance requires it, the ELM’s final invoice approval can generate the service receipt automatically.
Should each legal matter have its own purchase order?
Each legal matter should have its own purchase order only when its expected spend justifies the maintenance, often above about $50,000. Routine work usually runs on one blanket PO per firm per fiscal year.
What tolerance should apply when matching legal invoices to POs?
A legal invoice PO match should allow a small balance overrun, such as 5 percent or $1,000, whichever is lower. Supplier, legal entity, and PO status should allow no tolerance at all.
Why do legal invoices fail the PO match?
Legal invoices most often fail the PO match because the PO balance has run out, the PO closed at fiscal year-end, or the firm billed under a different vendor record. A pre-check in the ELM catches all three before AP sees the invoice.
Who approves a PO increase for a legal matter?
A PO increase for a legal matter is usually approved by the matter owner or budget holder and then processed by finance or procurement. Raising the request from the ELM alongside the budget change keeps both records aligned.
*This article is provided for general information only and does not constitute legal advice. Basla Solutions provides legal technology implementation and support services and does not practice law.*