Invoicing App Development

Businesses building invoicing platforms face a different engineering challenge than businesses using them. An AR automation SaaS targeting mid-market B2B companies needs to handle PEPPOL e-invoicing for EU customers, bidirectional ERP sync for invoice data reconciliation, and a dunning engine that adjusts contact cadence by customer tier and payment history. An embedded invoicing module inside a marketplace or SaaS platform needs multi-tenant invoice generation, white-label PDF output, and per-tenant tax calculation logic.

Scrums.com builds the invoice data models, e-invoicing integrations, payment rail connections, and AR workflow automation behind these platforms. Our engineering teams have built invoicing systems for FinTech companies, professional services SaaS platforms, and marketplace operators that need invoicing as a feature rather than a product.

Invoicing Platform Architecture

The complexity in invoicing platforms is in tax calculation accuracy, e-invoicing format compliance, and AR workflow state management, not the invoice PDF itself.

Invoice Data Model and Line Item Engine

Invoice records are modelled as immutable documents: once issued, corrections are handled via credit notes and re-issuance, not in-place edits. The line item engine supports flat fees, time-and-materials (hours x rate, with timesheet integration), milestone billing, and usage-based quantities pulled from a metering API. Tax rules are stored as versioned configuration (rate, jurisdiction, exemption categories), not hardcoded, so rate changes are applied without code deployment.

E-Invoicing and Structured Data Exchange

For EU and UK customers, the platform generates invoices in structured electronic formats: PEPPOL BIS Billing 3.0 (UBL 2.1 XML) for PEPPOL network delivery, Factur-X/ZUGFeRD (PDF/A-3 with embedded XML) for email delivery with machine-readable data, and EN 16931 semantic model compliance for cross-border EU trade. The PEPPOL access point integration handles SMP lookup for recipient endpoint discovery, document validation against the relevant PEPPOL BIS specification, and transmission acknowledgement tracking.

Accounts Receivable Workflow Engine

The AR workflow state machine tracks invoices through: Draft, Issued, Partially Paid, Paid, Overdue, Disputed, Written Off. Dunning sequences are configured per customer segment: enterprise customers on a manual escalation path, SME customers on automated email sequences with adjustable cadence. Each dunning contact is logged with timestamp, channel, and response outcome. Dispute handling creates a linked dispute record with evidence attachment, suspends the dunning sequence, and triggers an internal review workflow.

Payment Rail Integration and Reconciliation

Payment collection integrates with direct debit rails (GoCardless for BACS/SEPA Core, Stripe for ACH Debit), card payment for one-off settlement, and virtual bank account per customer for faster payment reconciliation via Modulr or Bankable. Inbound payments are matched to open invoices automatically using amount + reference number + IBAN source, with a matching confidence score that flags low-confidence matches for manual review rather than auto-posting incorrect allocations.

Types of Invoicing Platforms We Build

• B2B accounts receivable automation. Automated invoice generation from order/contract data, multi-channel delivery (PEPPOL, email, portal), dunning and collections workflow, payment matching and AR ledger reconciliation.
• PEPPOL e-invoicing platform. PEPPOL access point integration, BIS Billing 3.0 format generation and validation, SMP endpoint discovery, transmission audit trail, and recipient onboarding workflow for EU and UK mandates.
• Embedded invoicing for SaaS and marketplaces. Multi-tenant invoice generation with per-tenant branding, tax logic, and payment terms; white-label PDF output; tenant-scoped invoice portal for their end-customers.
• Professional services billing. Time-and-materials billing from timesheet or project management system integration, milestone billing, retainer drawdown tracking, and WIP reporting for IFRS 15/ASC 606 compliance.
• Government and public sector invoicing. Compliance with country-specific public procurement e-invoicing mandates (UK Crown Commercial Service, Pan-European PEPPOL), audit trail requirements, and purchase order reference matching.

Scrums.com's mobile app development teams build across the full range of invoicing and accounts receivable platform types. Start a conversation about your invoicing platform build.

Technology Stack for Invoicing Platforms

• Invoice generation. iText 7 or Apache FOP for PDF/A-3 output; UBL 2.1 XML generation with library validation against EN 16931 semantic model; Factur-X embedding for hybrid PDF/XML delivery.
• PEPPOL connectivity. OpenPEPPOL-certified access point integration (Storecove, Tickstar, or self-hosted Oxalis gateway); SMP lookup for endpoint discovery; AS4 transport protocol for document exchange.
• Tax calculation. Avalara AvaTax or TaxJar for US sales tax; EU VAT OSS rate lookup with member state rate tables; UK MTD VAT bridging data submission via HMRC Making Tax Digital API.
• Payment rails. GoCardless (BACS, SEPA Core Direct Debit, ACH); Stripe (card, ACH Debit, SEPA); Modulr/Bankable virtual IBANs for reconciliation-by-account; BACS submission file generation.
• AR ledger. PostgreSQL append-only ledger (invoices, credit notes, payments, allocations, write-offs as immutable entries); balance calculated from ledger, not stored as a mutable field.
• ERP integration. SAP IDoc/BAPI, Oracle Financials REST, NetSuite SuiteScript, Xero API, QuickBooks Online API for bidirectional sync of invoice and payment data.
• Workflow and notifications. Temporal or Conductor for durable dunning sequence orchestration (retries, delays, escalation); SendGrid/Postmark for email delivery with open/click tracking.

Regulatory Compliance for Invoicing Platforms

EU VAT and ViDA: Electronic Invoicing Mandate

The EU VAT in the Digital Age (ViDA) initiative mandates e-invoicing for intra-EU B2B transactions from 2030, with member states permitted to mandate earlier. Italy, France, Germany, Romania, and Poland already have or are implementing national mandates. The platform generates invoices that comply with EN 16931, the European standard for electronic invoicing, delivered via PEPPOL or through country-specific platforms (SDI in Italy, Chorus Pro in France). VAT OSS obligations for cross-border B2C digital services are handled via a quarterly return data aggregation and submission module.

UK Making Tax Digital for VAT

MTD for VAT requires businesses with taxable turnover above £90,000 to maintain digital records and submit VAT returns via HMRC-approved software. The invoicing platform maintains the digital audit trail HMRC requires (each invoice, credit note, and adjustment is a digital record) and submits the nine-box VAT return data via the HMRC MTD VAT API using OAuth 2.0 agent authorisation.

ASC 606 / IFRS 15: Revenue Recognition

For professional services and SaaS platforms, invoice issuance does not always coincide with revenue recognition. The platform maintains a separate revenue schedule linked to each invoice, recognising revenue against performance obligations (milestone completion, time elapsed for retainers) rather than at invoice date. This feeds the deferred revenue roll-forward that finance teams need for period-end close.

GDPR: Invoice Data Retention

UK and EU tax law requires invoice retention for 6 years (UK) and 5-10 years depending on member state (EU). GDPR grants data subjects a right to erasure, but this right does not override statutory retention obligations for financial records. The platform handles this tension by anonymising personal data not required for the tax record (names and contact details of individual employees named on invoices can be replaced with a persistent pseudonymous identifier), while retaining the financial data intact.