For flat-rate sole traders (paušalci)Available

An app for flat-rate sole traders: from invoice to KPO book

Issue an invoice or pro forma with an IPS QR code, send it via SEF or by email, and the KPO book fills itself. The home screen shows how close you are to the turnover limits and which tax deadline comes next.

Flat-rate sole traders
IT and freelance sole traders
Their accountants

Already have an account? Log in

We open your account and trial on request. Pricing is agreed with each company.

Illustration with sample data · the app interface is in Serbian

on every invoice and pro forma: IPS QR
fills itself from invoices and receipts: KPO
turnover limits, warning from 80%: 6M & 8M
send e-invoices without the portal: SEF

Invoices

An invoice or pro forma in half a minute

A flat-rate sole trader issues invoices and pro formas in the app, so the screen isn’t cluttered with options you don’t need.

Invoice and pro forma

Numbers are assigned automatically (001/2026, PR-001/2026), separately by type and year. Once the client pays, turn the pro forma into an invoice in one click.

PDF with IPS QR code

A PDF with your logo, the amount in words and the NBS IPS QR code, so the client pays by scanning it in mobile banking.

Send in one click

Clients on SEF receive the invoice through SEF, everyone else by email with the PDF. The public invoice link is protected by a PIN.

Payment reminders

The client gets an email three days before the due date, on the due date and seven days after. Switch reminders on once for the whole company.

Invoices for foreign clients

EUR, USD and CHF, with the PDF in Serbian, Serbian-English or English per client. In the KPO book they are converted to dinars at the NBS middle rate.

KPO and taxes

KPO book, taxes and limits

The KPO book keeps itself

Each issued invoice is a row in the book, and fiscal receipts are one row per day. Download the KPO form as PDF or CSV.

Taxes and contributions

Enter the amounts from your tax assessment by hand, and the app creates IPS QR payment orders and reminds you of the 15th-of-the-month deadline.

Tax calendar

A card with the next three deadlines for your tax status, with a notification 3 days before in the app and by email.

6 and 8 million limits

Tracks 6,000,000 RSD per calendar year and 8,000,000 RSD in any 365 days, retail included. It warns from 80% and never blocks invoicing.

E-invoices

SEF e-invoices without logging into the portal

Sending to SEF

Enter your SEF API key once; it is stored encrypted. Before sending, the app checks the data and translates SEF errors into plain Serbian.

Hourly status updates

Sent invoice statuses refresh automatically, so you see whether the client accepted or rejected the invoice.

Client checks

Find a client by tax ID or company number, and check whether they are on SEF and whether their account is blocked by the NBS.

Also included

Archive, cash register and mobile

Document archive

Folders for assessments, contracts and other papers, plus an archive book in the official form with a PDF copy.

Fiscal register coming soon

Solve Kasa is awaiting approval by the Tax Administration. Already today you can import fiscal receipts from another ESIR as PDFs, and they go into the KPO book.

On your phone

The app runs in the browser and installs on your phone like an app (PWA), without an app store.

How it works

For sole traders, step by step

Request a trial account
We open an organization for you with its own address (name.invoice.solve.rs).
Add your business
A tax ID lookup fills in your details, then you add your first client and service.
Issue your first invoice
Or a pro forma, and turn it into an invoice once it is paid.
Follow the book and limits
The KPO book, turnover limits and tax deadlines update on their own.

Notes

Good to know before you start

A flat-rate sole trader issues only invoices and pro formas in the app. Quotes, advance invoices and credit and debit notes are for businesses that keep books.
Bank, expenses, supplier invoices and reports are not shown to flat-rate sole traders.
You keep and download the KPO book as PDF or CSV. The app doesn’t file or certify it, and expenses are not part of the KPO book.
You enter the tax assessment data by hand; the app doesn’t fetch it from the Tax Administration.
The tax calendar moves deadlines off weekends to Monday but doesn’t account for public holidays. Treat it as a reminder.
The fiscal cash register (Solve Kasa) is awaiting Tax Administration approval and must not be used for live trading until then.

Works on desktop, tablet and phone – installs like an app (PWA)

Open invoice.solve.rs in your browser and add it to your phone’s home screen. Nothing to download from an app store. The interface is in Serbian; invoice PDFs can also be in English.

Desktop
Tablet
Phone
Each company’s data kept separate
Hosted in the EU (Frankfurt)

Questions

For sole traders: frequently asked questions

What can a flat-rate sole trader issue in the app?

Invoices and pro formas, with automatic numbering, an IPS QR code and a PDF. A pro forma becomes an invoice in one click once the client pays.

How do I send an e-invoice as a sole trader?

Enter your SEF API key and click “Send”. If the client is on SEF, the invoice goes through SEF; if not, by email with the PDF. The status then refreshes automatically.

How does the KPO book get filled?

On its own: every issued invoice is one row, and fiscal receipts are one row per day. Drafts, reversed invoices and pro formas are left out. Download the KPO form as PDF or CSV.

How does the app track the 6 and 8 million limits?

It adds up issued invoices and retail sales for the calendar year (6 million) and the last 365 days (8 million). From 80% of the threshold you get a warning, but invoicing is never blocked.

Can I invoice a foreign client in euros?

Yes. Invoices can be in EUR, USD or CHF, with the PDF in English or bilingual. In the KPO book they appear in dinars at the NBS middle rate on the date of supply.

Does the app pay my taxes for me?

No. Based on your tax assessment it creates IPS QR payment orders and reminds you of the deadline, and you pay from mobile banking.

How do I get an account and what does it cost?

There is no public sign-up: request a trial account and we open it for you. The price list isn’t published yet, and pricing is agreed with each company.

Available

Issue your first invoice on a trial account

Tell us what you do and whether you invoice companies through SEF, and we’ll open a trial account for you.

There is no public sign-up: we open the account and get back to you by email.