Case study

Markus Pausalkus

A modern platform for business management designed for freelancers, flat-rate entrepreneurs, and accounting agencies.

Project Overview

Markus Paušalkus is a production multi-tenant ERP built for the Serbian market, specifically for flat-rate entrepreneurs and the accounting agencies that serve them. It covers the full invoicing lifecycle - issuing invoices, proformas, advance invoices and credit/debit notes - with native integration to Serbia's System of Electronic Invoices (SEF / e-Faktura) via UBL 2.1 XML.

  • • Invoicing engine
  • • Flat-rate compliance
  • • Obligations & payment orders
  • • Bank statements & reconciliation
  • • Multi-tenant agency tooling
  • • Analytics
  • • Subscriptions & platform billing

Screenshots

Markus Pausalkus
Markus Pausalkus
Markus Pausalkus

Core Features

Invoicing engine

  • • Full document set: invoice, proforma, advance invoice, credit note, debit note, foreign-currency invoices.

Flat-rate compliance

  • • KPO book - a live merge of sent-invoice rows and manual entries, date-range filtering, CSV + PDF export.
  • • Turnover ledger.
  • • Fiscal cash-register daily-turnover log.

Obligations & payment orders

  • • Payment-order templates with recurrence rules.
  • • Auto-generated due obligations (daily cron), calendar view, overdue highlighting.
  • • Individual and batch email dispatch with PDF attachment.

Bank statements & reconciliation

Manual entry + XML import (Halcom format, Asseco), matching engine.

Analytics

  • • Per-customer revenue for any period.
  • • Ledger drawer (invoices + manual payments), manual payment entry, opening-balance carry-over
  • • CSV / PDF export, open-item statement (IOS) email dunning.

Subscriptions & platform billing

  • • Tiered flat-rate plans + per-client agency pricing.
  • • Trial handling with read-only enforcement on expiry, self-service activate / deactivate.
  • • Separate system invoices pipeline so the platform can bill self-registered tenants.
  • • Referral codes, account-block enforcement.

Tech Stack

Frontend

Next.js 16 • React • TypeScript • Tailwind 4 • shadcn/ui + Radix • TanStack Table • Recharts • next-intl

Backend

Next.js Server Actions • Better-auth • Drizzle • Better-auth • Nodemailer + Resend

Database

PostgreSQL • Drizzle ORM

Results & Impact

  • • ↓ 60% less manual data entry - invoice, KPO ledger, and payment records are generated from a single source
  • • Automated UBL 2.1 generation, VAT/exemption handling, and mod-97/PIB validation remove manual mistakes
  • • Bank reconciliation 10 × faster, one click confirms and closes the invoice/obligation, fully reversible
  • • Complete operations for a flat-rate company in one place
  • • One accounting agency runs all flat-rate clients from a single login
  • • Access from any location, whether you're on vacation or on a business trip

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