Automate accounts payable in construction: billing milestones, subcontractors and materials

Construction is a peculiar accounts payable case: each project is a business unit with its own budget, team and subcontractors. Central administration does not see the site; it sees invoices arriving in waves that have to be assigned to the right cost centre before the site manager either approves them blindly or rejects them because "they do not ring a bell".

Tools built for distribution or professional services do not contemplate partial billing milestones, retentions for performance bond, variable aggregate weight per truck or machine timesheet entries. Thesis: touchless AP does work in construction, but only if every invoice is matched line by line against its purchase order and delivery notes, and the milestone and contract checks stay with the people who signed them.

Why construction is different from the rest of AP

According to the National Confederation of Construction (CNC) and the Construction Economic Survey by INE, the sector keeps a relevant weight on Spanish GDP and employs several hundred thousand people. What matters for AP is the cost composition: a very large share is subcontracting and materials with daily delivery frequency.

The five traits that make this case different:

• High and dispersed volume per project. 300-600 invoices/project per month is not exceptional. With three live projects, administration receives between 900 and 1,800 monthly documents that must be allocated to the correct cost centre before being touched.
• Subcontractors invoicing per partial milestone. The subcontractor bills 30% of the chapter this month, 25% the next, until liquidation. Each invoice goes against a milestone signed by the site manager that must reconcile with the original contract.
• Materials with daily delivery notes and agreed prices. Cement by tank, steel by truckload, aggregates by volume. The supplier delivers each day, the delivery note is signed by whoever receives on site, and at month-end the invoice arrives bundling 30 delivery notes.
• Equipment rentals with variable hours. A backhoe works 7 hours Monday, 3 Tuesday and 0 Wednesday. The renter bills the hours their record says; the site manager has their own record. When they do not match, someone overpays.
• Multi-project with duplicates and cost centres. The same supplier delivers to two projects and issues one invoice. Or worse: issues two invoices for the same delivery arriving at different inboxes. Without a project tag, everything goes to the same account.

The result is that an admin team of two or three people spends 100-150 hours a month just classifying invoices by project, chasing milestones and disputing differences. And a significant percentage of discrepancies still slip through: the typical avoidable overrun sits between 5% and 8% of project cost when there is no systematic cross-checking.

Classic problems in construction AP

The following table summarises the six most frequent blockages in Spanish construction companies. None is solved by a classic OCR or a generic approval workflow.

Problem	Typical frequency	Impact
Subcontractor bills more than certified	10-20% of subcontractor invoices	Advance payment without matching bond
Materials at a price different from agreed	15-25% of fresh-material lines	Direct undetected overcost
Duplicates across projects from the same supplier	3-5% of invoices	Double payment without a project tag
Partial milestones with no linked contract	Common when the contract lives on paper	Impossible to audit real project progress
Equipment rental with mis-billed hours	20-30% of monthly timesheets	Inflated hour cost vs real timesheet
Transport with inflated mileage and surcharges	10-15% of logistics invoices	Margin eroded in logistics chapter

Subcontractors and partial milestones

Matching the subcontractor invoice is the most sector-specific and where the biggest savings live. The logic differs from classic three-way matching: here the "delivery" is a milestone, a percentage of executed work signed by the site manager. The invoice must reconcile with the milestone and with the framework contract signed at the start.

• Original contract. Defines chapters, measurements, unit prices and bond retentions.
• Partial milestone. Each month, the site manager signs what percentage of each chapter has been executed.
• Subcontractor invoice. Must reflect exactly what was certified, applying contract prices and discounting the retention.

Without a system, someone opens three documents in parallel and signs because "they have seen it before". ininvoice does not read contracts or milestone certificates. What it checks automatically is the subcontractor invoice against its purchase order and, where there is one, its delivery note, line by line. Checking the milestone against the contract, and the retention, stays with the site manager, and a person approves every invoice.

Materials and multiple delivery notes

The second large chapter is materials: cement, steel, aggregates, brick, prefab, fittings. The usual dynamic:

• Framework order. The site manager agrees estimated volume and unit prices (cement bag, steel ton, concrete m³).
• Daily delivery note. Each delivery generates a note signed by the foreman. Sometimes paper, sometimes digital.
• Monthly invoice. The supplier bundles the period's notes. If not cross-checked line by line, anything from the road to the invoice slips through unfiltered.

The universal line-by-line variance rule applies as-is here: never compare header totals. You must check unit price and quantity of each line against agreed price and the accumulated quantity from the period's delivery notes. Only this way do silent overcosts surface.

Equipment rental and timesheets

Rented equipment (backhoes, cranes, dumpers, platforms) is billed by effective hours or days. The recurring conflict: the renter sends their hours record, the site manager has their own, and between them there is usually a 5-15% difference nobody claims.

ininvoice does not read timesheets. If the rental is ordered with a purchase order, the renter's invoice is compared line by line against it; checking the hours billed against the site's own record stays with the site manager.

The touchless flow adapted to construction

A generic touchless flow does not work here. Five phases must be adapted:

1. Multi-project ingestion. Each project has its own inbox or alias, and invoices from every mailbox land in the same queue without anyone forwarding anything. ininvoice does not assign a project, site or cost centre; that allocation is done in the ERP.
2. OCR/IDP with document typology. A subcontractor invoice, a material invoice and an equipment rental invoice look very different. The extractor reads each one line by line, whatever its layout.
3. Three-way matching. For every invoice: purchase order vs delivery note vs invoice, line by line. Milestone certificates, contracts and machine timesheets are not read by ininvoice; those checks stay with the site team.
4. Who answers each exception. A deviation on a subcontractor invoice is a question for the site manager who signed the milestone. A material price deviation is one for procurement or HQ. A possible cross-project duplicate is one for administration. ininvoice shows the type and the reason of each exception; your team decides who follows it up, and a person approves the invoice.
5. Export to accounting and project cost control. Once a person has approved them, invoices are exported as a CSV or Excel file that the ERP or project software imports, and from there they feed the actual-vs-budget cost control.

This flow leaves humans where they add value: the site manager validates milestones, procurement renegotiates material prices, administration reviews exceptions and approves invoices.

Late payment and legal payment term

The construction sector is especially exposed to operational late payment. Between companies, Article 4 of Spanish Law 3/2004 on late payment sets a payment term of 30 days from receipt of the goods or services, which the parties can extend by agreement up to a maximum of 60 days. When the client is a public administration, the terms of Law 9/2017 on Public Sector Contracts apply. Check the term set in each contract with your legal adviser.

Manual AP delays invoice recognition: if it takes 9-14 days to enter the ledger because someone had it in a tray, the legal payment term starts running against you. Matching invoices as they arrive, instead of when someone gets to the tray, gives real margin to meet deadlines without paying early or incurring late-payment interest.

Integration with construction ERP

AP does not live in isolation. The invoice arrives, gets reconciled and approved, and the approved data feeds the project cost control that compares real milestones with budget. Construction companies with a mature stack typically combine:

• Budget and quantity survey software with products like Presto, Menfis, Cype Arquimedes or equivalents. They provide the original contract with chapters and unit prices.
• ERP and accounting like A3 ERP, Sage Construction, Datisa or vertical packages. They import the approved invoices from AP as a CSV or Excel file.
• AP automation layer between the supplier inbox and the ERP. ininvoice lives here: ingestion, reading, three-way matching, approval by a person and export of approved invoices.

The idea is not to duplicate masters. Projects and cost centres are kept and allocated in the ERP. Subcontractor contracts live in project management software or the ERP, not in AP; ininvoice does not read them. The AP layer reads, matches and, once a person has approved, exports.

Verifactu and construction

When obliged material suppliers and subcontractors start issuing with Verifactu and B2B e-invoicing, construction companies will receive more invoices with structured data. They are two rules with different calendars. B2B e-invoicing (Law 18/2022, developed by Royal Decree 238/2026) applies from 6 October 2027 to companies with turnover above EUR 8 million and from 6 October 2028 to everyone else, according to the AEAT implementation calendar. Verifactu (Royal Decree 1007/2023) requires the issuer to have its billing system adapted before 1 January 2027 if it pays corporate income tax and before 1 July 2027 in all other cases, after Royal Decree-law 15/2025; businesses keeping their VAT books through the SII are outside it. On 5 October 2026 the Ministry of Finance announced a delay of Verifactu to October 2028, which for now is only an announcement. The recipient of the invoice has no Verifactu obligation.

For a construction company, the practical job does not change: every invoice received, whether it arrives as a PDF, an image or a scan, has to match its purchase order and delivery note line by line before it is paid. If the supplier uses the VERI*FACTU mode, its billing records also reach the AEAT when issued, so a divergence between your books and what the supplier invoiced is easier to spot.

Estimated case: construction company with 3 concurrent projects

Indicative figures for a construction company with 3 open projects, 1,200 aggregated invoices/month and two admin people.

Metric	Manual AP	With ininvoice (estimate)
Hours/month on capture, sorting and reconciliation	~120 h	~35 h (exceptions only)
Average invoice → ledger time	9-14 days	<48 h
Discrepancies detected	Only what someone reviews by hand	Every matched line is checked
Imputable AP staff cost	~EUR 2,400/month	~EUR 700/month
AP software cost	EUR 0	Tailored pricing
Estimated AP staff saving (before software)	—	~EUR 1,700

This does not include recovered project overruns. If the company cuts half a point of the 5-8% avoidable overrun on EUR 6M/year of execution, that is an additional EUR 30,000 typically lost in the "we do not know exactly where the margin goes".

Checklist for the admin manager

Ten concrete actions an admin manager can kick off this quarter without slowing the site:

1. Inventory the real volume: how many invoices/month each project receives and from how many different suppliers and subcontractors.
2. Identify the top 10 subcontractors by amount and the top 10 material suppliers by volume. They usually do not overlap.
3. Measure how much time administration spends classifying by project vs resolving discrepancies.
4. Audit a real month of milestones: how many are linked to a contract and how many the site manager signs "because they have seen them before".
5. Compute real-cost vs budget deviation by project and chapter. The dispersion between chapters is usually telling.
6. List suppliers with variable weight (aggregates, concrete) vs fixed unit price (steel per kg, prefab per unit). Decide whether one tolerance policy fits every family.
7. Confirm with procurement which contracted prices exist by framework and how they are kept up to date.
8. Confirm with the accounting team or firm how approved invoices are imported into the ERP (A3, Sage, Datisa) and the project management software.
9. Agree who answers each exception: the site manager, procurement or administration.
10. Pilot with one project before rolling out. Measure KPIs for 4-6 weeks.

Frequently asked questions

Does this work if my subcontractors still send milestones in Excel?

ininvoice does not read milestone certificates or contracts. It reads the subcontractor’s invoice and matches it against its purchase order and delivery note when there are any; checking the invoice against the signed milestone stays with the site manager. You do not need project software to start.

What about bundled invoices mixing several projects?

ininvoice does not split invoices by project or assign them to one; that allocation is done in the ERP. If the supplier does not differentiate projects on the invoice, ask them to; without a project reference, there is no cost control per project.

How are bond retentions handled in subcontractor invoices?

ininvoice does not store contract retention percentages or apply them. Checking that the invoice deducts the right retention stays with whoever validates the milestone; it is one of the points where advance payment slips through most.

Do I need a formal contract with each subcontractor?

For your own control, yes: the framework contract with measurements, unit prices and retention is what the milestone is checked against. For ininvoice’s matching, what counts is the purchase order: the invoice is compared line by line against it and against the delivery note.

What integrations does it have with construction ERP?

ininvoice exports approved invoices as a CSV or Excel file that your ERP imports. There is no native connector with A3, Sage, Datisa, Presto, Menfis or Cype: the file goes in through each ERP's standard import.

How long does it take to go live in a construction company?

It starts when you connect the inbox: without implementation or a consultant, it is up and running in 24–48 hours. Rolling out to every project depends on volume and subcontractor heterogeneity.

Does it replace the ERP or the project management software?

No. ininvoice is pure AP automation. It sits between the supplier inbox and your ERP or project software. Approved invoices are exported as a CSV or Excel file that A3, Sage or Datisa can import.

Three things to remember

Construction is not just another AP case. It is one of the hardest there is and, for the same reason, where there is most room for good automation.

1. Manual AP at construction companies with 3+ projects silently eats whole points of margin.
2. Generic touchless will not do. Every invoice must be matched line by line against its purchase order and delivery note, while milestone and timesheet checks stay with the site team.
3. The stack that works is light: supplier inbox → AP automation layer → construction ERP. The budget and survey software feeds contracts in parallel. No big projects.

If you want to see how your flow looks with one real project, try ininvoice with your own invoices. Pricing is tailored: a proposal within 48 hours of seeing your invoices.

Related content

• Three-way matching: cross-checking invoice, PO and delivery note line by line
• Touchless accounts payable: what it means and how to measure it
• Managing invoices in construction: base guide by supplier
• Invoice automation rate: how to measure the touchless rate
• IDP vs OCR: why the difference matters in AP