Invoice Approval Workflow: How to Design and Automate AP Approvals
By Kirill Stolbushkin
Short answer: An invoice approval workflow is the path a supplier invoice follows from the moment it arrives to the moment it is approved for payment: capture it, check it, match it, code it, route it to the right approver, handle exceptions, and post it. The center of the workflow is the approval matrix, a short set of rules that decides who approves what. Get the matrix right and most of the workflow designs itself.
We gave invoice approval a short section in 5 workflows you can automate this week. This is the full version, for the person who actually has to design it.
What the invoice approval workflow covers
The workflow starts when an invoice arrives and ends when it is approved and posted, ready for payment. It sits between two other processes:
Before it: purchasing. Someone requests a purchase, it gets approved, and a purchase order goes to the supplier. That is procure-to-pay territory, and our procure-to-pay use case covers it end to end.
After it: the payment run. Releasing money should be its own authorization, not a side effect of approving an invoice.
Keeping the scope this tight makes the workflow easier to design and easier to audit.
The invoice approval workflow, step by step
Step 1: Capture every invoice in one place
Pick one intake point, usually a shared AP inbox or an upload folder, and send every supplier there. Invoices that land in a manager's personal inbox are the ones that get paid late. At capture, pull out the fields everything else depends on: supplier, invoice number, invoice date, due date, amount, tax, and PO number if there is one.
Step 2: Check it before anyone approves it
A few checks catch most problems before they waste an approver's time:
The supplier exists in your vendor list and the bank details match what you have on file.
The invoice is not a duplicate. Check the same supplier and invoice number, and also the same amount on a close date.
The totals and tax add up.
Step 3: Match it to the purchase order
If the invoice has a PO, match them. A two-way match compares the invoice to the PO: same supplier, same items, same prices. A three-way match adds the goods receipt, so you only pay for what actually arrived. Set a tolerance for small differences. Inside the tolerance, the invoice moves on. Outside it, it becomes an exception.
Invoices without a PO, such as utilities, software subscriptions, and professional services, skip the match and go to the budget owner for approval instead.
Step 4: Code it
Assign the general ledger account, cost center, and project if you track them. Software can suggest the coding from past invoices from the same supplier, but a person should confirm anything unusual.
Step 5: Route it with the approval matrix
The matrix picks the approver, or approvers, based on the invoice. More on building it below.
Step 6: Approve, reject, or ask a question
Approvers should see the invoice, the coding, and the supporting documents in one place, and approve the actual invoice, not an email that describes it. They need three options: approve, reject with a reason, or send a question back to AP. Every decision gets a name and a timestamp.
Step 7: Post and hand off for payment
Once all required approvals are in, AP posts the invoice to the ledger and it joins the next payment run. The person who releases the payment should not be the person who approved the invoice.
How to build an approval matrix
An approval matrix is a table that maps invoice attributes to the approvers required. It turns routing from a judgment call into a lookup, and it is the first thing an auditor asks to see.
Most small teams only need a handful of rules. The attributes that usually matter:
Amount: bigger invoices need more senior approval.
PO or non-PO: a matched PO invoice has already been approved once, at the purchase stage.
Cost center: the budget owner approves spend against their budget.
Supplier risk: new suppliers and changed bank details need extra checks.
Entity: if you run more than one company, each entity has its own approvers.
An example, with thresholds you would set yourself:
PO invoice that matches within tolerance: no further approval, AP posts it.
Non-PO invoice under your first threshold: budget owner approves.
Non-PO invoice between your first and second thresholds: budget owner, then finance lead.
Any invoice above your second threshold: add the CFO or owner.
New supplier or changed bank details: finance lead confirms by phone, using contact details you already had, before any payment, whatever the amount.
A few rules of thumb. Keep the number of amount bands small, and put each threshold where the risk actually changes. Name a delegate for every approver, so a vacation does not stop the queue. Review the matrix at least once a year and whenever someone changes roles.
Exceptions are the real workflow
Clean invoices are easy. Most of the design work is in the exceptions:
No PO when one was required: back to the requester to raise a PO, or to the budget owner to approve it as a non-PO invoice.
Price or quantity mismatch: to the buyer or requester, who either confirms the difference or asks the supplier for a credit note.
Suspected duplicate: held by AP until confirmed.
No goods receipt: to the person who ordered it to confirm what arrived.
Approver does not respond: a reminder after a set number of days, then reassignment to the delegate.
Rejected: back to AP with the reason, and AP tells the supplier.
Write each exception path down. If an exception only exists in someone's head, it will be handled differently every time.
Controls worth keeping in a small team
You do not need an enterprise control framework to run AP safely, but a few controls are worth keeping at any size:
Separate duties: whoever enters an invoice should not approve it, and whoever approves it should not release the payment.
Approve the invoice itself: not a forwarded email or a chat message.
Keep an audit trail: who approved what, when, and against which rule.
Verify bank detail changes out of band: a call to a known contact, never a reply to the email that asked for the change. This is the classic way invoice fraud gets in.
If you are in scope for SOX or heading toward an audit, our guide to SOX internal controls documentation explains how these controls get documented and tested.
How the invoice approval workflow maps to BPMN
The workflow translates directly into a BPMN model. The BPMN symbols cheat sheet explains each shape.
Message start event: a new invoice arrives.
Tasks: capture, check, match, and code, in an AP lane.
Exclusive gateways: PO or non-PO, match inside or outside tolerance, and which amount band applies.
Approver lanes: budget owner, finance lead, and CFO, with sequential approvals for larger invoices.
Timer boundary events: a non-interrupting timer sends a reminder, and an interrupting timer reassigns the task to the delegate.
Loops: rejections and questions route back to AP.
End event: posted and ready for payment.
Laid out in swimlanes, the model also shows where segregation of duties holds and where it does not.
How to model and automate this in Vevos
Write your approval policy the way you would explain it to a new AP clerk, and Vevos turns it into a BPMN 2.0 model with the lanes, gateways, and timers already in place. For example:
"When an invoice arrives, AP checks the supplier and looks for duplicates. If it has a PO, AP matches it. If it matches, AP posts it. If not, the buyer reviews the difference. Non-PO invoices go to the budget owner. Anything above our second threshold also goes to the CFO. If an approver has not responded in three days, they get a reminder, and after five days it goes to their delegate."
Review the model with AP and a couple of approvers, then fix what does not match reality.
To see what the automated version looks like, our invoice processing use case shows an example app with invoice upload, AI extraction, suggested GL coding, and exception review.
You can map your own policy with the free AI process mapper, no account needed. Modeling starts free, with $9 and $29 plans for more room. Having Conductor Agents build and deploy a working approval app from your reviewed model starts on Tempo at $199/month. See the pricing page for details.
FAQ
What is an invoice approval workflow?
It is the set of steps a supplier invoice goes through between arriving and being approved for payment: capture, checks, PO matching, coding, routing to approvers, exception handling, and posting. The workflow decides who reviews each invoice, in what order, and what record each decision leaves.
What is an approval matrix in accounts payable?
A table of rules that maps invoice attributes, such as amount, cost center, supplier, and entity, to the people who must approve. It makes routing consistent, keeps approvals within each person's authority, and gives auditors one document to check against.
What is the difference between two-way and three-way matching?
Two-way matching compares the invoice with the purchase order. Three-way matching also compares it with the goods receipt, so you confirm the items actually arrived before you pay. Three-way matching is worth it for physical goods. For services, two-way matching plus the budget owner's approval is often enough.
How do you handle invoices without a purchase order?
Route them to the budget owner for the cost center, with extra approval above your thresholds. If a PO was required by policy and is missing, send the invoice back to the requester rather than approving around the policy.
Should the person who approves an invoice also release the payment?
No. Keep approval and payment release as separate steps with separate people, even in a small team. If that is not possible, add a second review for payments above a threshold.
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