If you supply services to a large resources company, your invoice probably goes through SAP Ariba or the Coupa supplier portal, and it gets paid only when it matches the buyer's purchase order and their record of what was received. Most rejected or held invoices come down to one of three things: the invoice doesn't match the PO lines, the buyer hasn't receipted or approved the work yet, or the supporting documents, such as approved timesheets or service records, aren't attached. For mining contractors, plant hire and labour hire firms, the root cause usually sits further back: the same timesheets and dockets are keyed separately into payroll, job costing and the invoice, and the three versions don't agree. This article covers why portal invoices get rejected and how to get one set of approved hours feeding all three.
How portal invoicing works
Big buyers use procurement systems so that they only pay for what was ordered and received. The basic flow is the same in Ariba and Coupa:
- Purchase order. The buyer issues a PO with lines, quantities, rates and tax codes.
- Receipt or service sheet. The buyer confirms the goods arrived or the services were done. For services this is often a service entry sheet.
- Invoice. You create the invoice against the PO, usually by "flipping" the PO in the portal so the lines carry across, and attach the supporting documents.
- Match and approve. The buyer's system compares the invoice with the PO and the receipt. Matches move to payment. Differences go on hold or back to you.
What the buyers' own guides say
The buyers' supplier guides are the best source on what they expect. Two examples:
- BHP publishes Ariba guides for suppliers. They describe the service entry sheet as confirming that the services agreed in the PO have been completed, and say an invoice created alongside a service sheet is held in Ariba until BHP approves the service sheet.
- Glencore's Coupa supplier portal training says an invoice can only be created once the goods or services have been delivered and received, that purchase orders can't be consolidated into one invoice, and that the invoice must carry attachments, including the delivery or service record approved by the administrator. It also says to delete PO lines that aren't being invoiced rather than putting zero in the quantity or price.
Each buyer sets its own rules, so read the guide for every customer you invoice through a portal.
Why Ariba and Coupa invoices get rejected
Going by the buyers' guides and the issues suppliers commonly hit, the usual reasons are:
- PO mismatch. The quantity, rate, tax code or line description on the invoice doesn't match the PO line. Charging more hours than the PO allows is a classic one.
- No receipt yet. The work hasn't been receipted or the service sheet hasn't been approved, so there is nothing to match against.
- Missing or wrong attachments. No approved timesheet, docket or service record, or one that doesn't agree with the invoice.
- Wrong PO or wrong entity. Hours charged to an expired PO, a PO that has run out of value, or the wrong company name.
- Combined invoices. Several POs put on one invoice when the buyer wants one invoice per PO.
- Duplicates. The same work invoiced twice, often after a correction.
Each of these sends you back to correct and resubmit, and the payment clock starts again.
The real problem: three versions of the same hours
For a contractor, the hours and dockets from site have to go three places:
- Payroll, where the hours become pay under your enterprise agreement or award, with shift, overtime and site allowances.
- Job and plant cost, where the hours and machine time are costed to the right job, contract and asset.
- The customer invoice, where the same hours are charged against the right PO lines at the contract rates, with the approved timesheet attached.
In many businesses each of those is a separate re-key from paper or a spreadsheet. A supervisor's correction makes it into payroll but not the invoice. A docket is coded to the wrong PO. A machine hour is charged but never costed. The portal then rejects an invoice that doesn't match the approved timesheet the buyer already holds.
Payday Super, which started on 1 July 2026, adds pressure on the payroll side: super for each pay run has to reach funds within 7 business days of payday, so late timesheet corrections now affect super as well as pay.
Getting one set of hours to feed everything
The aim is that hours and dockets are captured once, approved once, and every other step reads that approved record.
- Capture against the PO from the start. Timesheets and dockets record the customer, PO and PO line as well as the job, worker and machine. Digital docket and timesheet apps can do this, if the PO lines are loaded into them.
- Approve once. The client's sign-off on the timesheet is the approval that drives pay, cost and invoice. Corrections after approval go through the same path.
- Feed payroll. Approved hours go into your payroll system with the right pay codes, so pay and super come from the same hours that are billed.
- Feed job and plant cost. The same hours and machine time reach job costing, so margin by contract is known before month end.
- Build the invoice from the PO. The invoice is prepared line by line against the PO, checked against the remaining PO value, and the approved timesheet or docket is attached automatically.
- Check before you submit. A simple pre-check flags hours with no PO, PO lines that would be exceeded and missing approvals, before the portal does.
- Record the outcome. Portal status (approved, held, rejected) comes back into your accounts or a dashboard, so debtors know what is stuck and why.
Some of this your existing tools may already do. Ariba and Coupa both offer ways for suppliers to send invoices electronically, and some job and docket apps connect to Xero or MYOB. The gaps are usually between them: PO lines that never reach the docket app, approved hours that don't reach payroll, invoices that are typed into the portal by hand. Those gaps are what business process automation and systems integration work is for.
Frequently asked questions
Why was my Ariba invoice put on hold?
The most common reasons are that the buyer hasn't approved the service entry sheet or receipt yet, or the invoice doesn't match the PO lines. Check the invoice status and any comments in the portal, then check the buyer's supplier guide.
Can I put several POs on one Coupa invoice?
Usually not. Glencore's Coupa guide, for example, says purchase orders can't be consolidated and each must be invoiced separately. Check the rules for each customer.
Do I need to attach timesheets to a portal invoice?
Many buyers expect approved timesheets, dockets or service records to support a services invoice, and some portals won't accept the invoice without an attachment. The buyer's supplier guide will say what they need.
Can Xero or MYOB send invoices straight to Ariba or Coupa?
Not on their own. Both portals accept electronic invoices, but the invoice has to match the buyer's PO lines, which your accounting system doesn't hold. That matching step is usually where a connection between your job system, accounts and the portal is needed.
We only invoice one portal customer a month. Is this worth automating?
Probably not. If a person can match a handful of invoices carefully each month, that's fine. It becomes worth fixing when rejections are frequent, the same hours are keyed three times, or payment is regularly delayed by resubmissions.
If your portal invoices keep bouncing and your timesheets are keyed more than once, book a free initial chat. We'll tell you honestly whether it's a process fix or a systems one. For related reading, see what your labour actually costs per job.