In this guide · 8 sections
- 01Start with the rules: who approves what
- 02What an approval workflow needs to do
- 03Options: accounting software, Microsoft 365 or a custom app
- 04Linking approved purchase orders to supplier bills
- 05Fraud controls worth building in
- 06Rolling it out without slowing the business
- 07Do it yourself or get help?
- 08Frequently asked questions
Short answer
Write down approval limits by amount (for example, managers up to S$2,000, a director above), route every request through one system that records who approved what and when, and only pay bills that match an approved purchase order. Xero, Zoho Books and Microsoft Teams can handle simple versions.
Start with the rules: who approves what
The software is the easy part. Agree the rules first, keep them to one page, and make sure the directors sign off on them.
| Amount (per purchase) | Who approves | Extra requirement |
|---|---|---|
| Up to S$500 | Team lead | Within monthly budget |
| S$500 to S$2,000 | Department manager | Purchase order raised before ordering |
| S$2,000 to S$10,000 | Director | At least two quotes attached |
| Above S$10,000 or any new supplier | Two directors | Supplier checks and contract review |
Add rules for categories that carry more risk regardless of amount, such as software subscriptions (which renew silently), anything paid to a new supplier, and anything paid overseas.
What an approval workflow needs to do
Minimum features
If a tool cannot keep an audit trail that approvers cannot edit, it is a messaging tool, not an approval system.
Options: accounting software, Microsoft 365 or a custom app
Purchase orders in your accounting software
- Xero: draft, submit for approval, approve, then copy to a bill
- Zoho Books: purchase orders and purchase approvals from Professional
- Approved orders link straight to supplier bills
- Limited routing by amount
Best for: Small teams where a director approves most orders.
Microsoft 365: Teams Approvals or Power Automate
- Teams Approvals app available to all Teams users
- Power Automate flows can route by amount
- Records kept in Microsoft's Dataverse
- Needs work to push results into accounting software
Best for: Businesses already living in Teams and SharePoint.
Custom approval app
- Rules, budgets and multi-level routing built for you
- Creates the purchase order in Xero or Zoho Books automatically
- Mobile-friendly for approvers on the move
- Higher upfront cost
Best for: Many requesters, several cost centres or project budgets.
Xero's purchase orders API shows the statuses an order moves through (draft, submitted, authorised, billed, deleted), which is what a custom app or automation updates. Microsoft's Approvals app admin page says the app is available to all Teams users and stores approvals in the default Dataverse environment. For flows beyond simple sign-offs, our Power Automate vs Zapier guide compares the two tools.
Linking approved purchase orders to supplier bills
The point of a purchase order is that the bill can be checked against it. This 'matching' step catches overcharges, duplicate bills and invoices for things nobody ordered.
Raise the purchase order before ordering
The supplier receives the PO number and is asked to quote it on the invoice.
Record what was received
For goods, someone confirms delivery and quantity; for services, the requester confirms the work was done.
Turn the approved order into a bill
In Xero, an approved purchase order can be copied to a bill; Zoho Books links bills to purchase orders in the same way.
Check the bill against the order
Same supplier, same amounts and quantities. Anything over a small tolerance goes back to the approver.
Pay only matched bills
Unmatched bills wait. This rule is the one that stops most fraud and duplicate payments.
Zoho Books' Singapore pricing lists purchase orders and purchase approvals on the Professional plan, S$30 a month billed yearly or S$36 monthly, excluding GST, as of October 2026.
Fraud controls worth building in
Approval workflows are also fraud controls, but only if a few duties are kept apart. Fake supplier invoices and bank detail change requests are among the most common frauds against small businesses; our guide to fake supplier invoice fraud covers the warning signs.
Controls that work
- Requester, approver and payer are different people
- Supplier bank details changed only after a call to a known number
- New suppliers checked (ACRA search, address, phone) before the first order
- Approvers see the quotes and the budget remaining
Gaps to close
- One person can create a supplier, approve and pay
- Requests split into smaller amounts to stay under a limit
- Approvals given in chat with no record
- Bills paid without a matching order 'because it's urgent'
Rolling it out without slowing the business
Approvals fail when they are slower than a WhatsApp message. Keep the request form short, let approvers act from their phones, and set a response target. Start with one department for a month, then extend.
Do it yourself or get help?
If one director approves everything, Xero or Zoho Books purchase orders plus a written policy are often enough, and you can set them up yourself. Multi-level routing, project budgets and mobile approvals that write back into the accounts are where help pays off.
Our Custom Business App (from S$4,900) can combine requests, approvals, purchase orders and budgets in one browser-based system connected to Xero, QuickBooks or Zoho Books, with roles for staff and managers. For a single flow, such as a form that routes approvals by amount and creates the PO, Workflow Automation is S$390 per workflow. IT Sorted is a Singapore-based team of developers with over 10 years of experience; you pay upfront, send the brief in writing and follow progress on your order page.
Frequently asked questions
It is the set of rules and steps a purchase goes through before money is committed: a request with details and quotes, approval by the right person based on amount and category, a purchase order to the supplier, and matching the supplier's bill to that order before payment. Each step is recorded.
Yes. In Xero you can save a purchase order as a draft or submit it for approval; once approved it can be sent to the supplier and later copied to a bill. Xero does not route approvals by amount on its own, so larger businesses often add an approval app or automation.
For simple approvals, yes. Microsoft says the Approvals app is available to all Teams users and keeps a record of each request and decision. For routing by amount or pushing approved orders into accounting software, you need a Power Automate flow or a separate app.
There is no standard; base them on your cash flow and how often you buy. A common pattern is team leads for small amounts, managers for mid-sized purchases with a purchase order, and directors for large amounts or any new supplier, with two quotes above a set value.
By separating duties and refusing to pay bills that don't match an approved order. If the person approving purchases cannot also add suppliers, change bank details or release payments, and every bill needs a matching order, fake invoices and bank detail scams are much harder to push through.