Invoice system

The invoice module generates sales documents directly in WooCommerce. It supports four document types, automatic numbering and PDF.

Document types

VAT invoice

A standard VAT invoice containing:

• seller and buyer data (including VAT IDs for both parties)
• line items with name, quantity, net price, VAT rate, VAT amount and gross price
• summary with VAT rate breakdown
• invoice number, issue date and sale date
• payment terms and payment method

Correction invoice

A correction document for a previously issued invoice. It contains:

• number and date of the corrected invoice
• line items before and after correction
• value difference
• reason for correction

A correction invoice can be issued from the order panel or via the REST API.

Receipt

A simplified sales document for individual customers (without buyer VAT ID). Contains line items with gross prices and a summary.

Packing slip

An external release document attached to the shipment. Contains a list of products, quantities and any order notes. Does not include prices.

Configuration

Go to WooCommerce > Settings > Polski > PRO Modules > Invoices.

Seller data

Field	Description
Company name	Full name of the seller company
VAT ID (NIP)	Tax identification number of the seller
Address	Street, number, postal code, city
Bank account number	Account number for wire transfers
Contact email	Email address displayed on the invoice

Numbering

The plugin offers several invoice numbering strategies:

Strategy	Format	Example
Annual	FV/{number}/{year}	FV/1/2026
Monthly	FV/{number}/{month}/{year}	FV/1/04/2026
Continuous	FV/{number}	FV/1
Custom pattern	User-defined	FV/2026/04/001

Available tokens in the custom format:

• {numer} - sequential invoice number (reset according to strategy)
• {rok} - four-digit year
• {miesiac} - two-digit month
• {dzien} - two-digit day
• {id_zamowienia} - WooCommerce order ID

Automatic generation

The plugin can automatically generate an invoice when the order status changes to “Completed”. Enable the Automatic invoice generation option in the module settings.

You can also configure automatic sending of the invoice PDF as an attachment to the WooCommerce “Order completed” email.

PDF generation

Invoice PDFs are generated using the TCPDF library. The PDF template includes:

• company logo (optional, configurable in settings)
• seller and buyer data
• line items table with VAT columns
• summary with VAT rate breakdown
• footer with company data

Fonts

The plugin uses the DejaVu Sans font, which supports Polish diacritical characters. No additional configuration is required.

Invoice status

Each invoice goes through a status lifecycle:

Draft (Szkic) → Issued (Wystawiona) → Sent (Wysłana) → Paid (Opłacona)
                                                      → Cancelled (Anulowana)

Status	Description
Draft	Invoice created but not yet issued. Can be edited
Issued	Invoice issued with an assigned number. Cannot be edited
Sent	Invoice sent to the customer (email or KSeF)
Paid	Invoice paid
Cancelled	Invoice cancelled. Requires issuing a correction

Order panel

In the WooCommerce order admin panel, the module adds an “Invoices” meta box with the following functions:

• Issue invoice - generates an invoice based on order data
• Download PDF - downloads the invoice in PDF format
• Send to customer - sends the invoice via email
• Issue correction - creates a correction invoice
• History - list of all documents associated with the order

VAT on line items

Each invoice line item contains detailed VAT data:

• unit net price
• VAT rate (23%, 8%, 5%, 0%, exempt, not applicable, reverse charge)
• unit VAT amount
• net value
• gross value

The plugin automatically recognizes the VAT rate from the WooCommerce Tax configuration. It supports multiple VAT rates on a single invoice with correct totals.

REST API

The module provides REST API endpoints for managing invoices programmatically.

List invoices

GET /wp-json/polski-pro/v1/invoices

Query parameters:

Parameter	Type	Description
order_id	int	Filter by order ID
status	string	Filter by status (draft, issued, sent, paid, cancelled)
type	string	Filter by type (invoice, correction, receipt, packing_slip)
date_from	string	Date from (YYYY-MM-DD)
date_to	string	Date to (YYYY-MM-DD)
per_page	int	Results per page (default 20)
page	int	Page number

Create invoice

POST /wp-json/polski-pro/v1/invoices

{
    "order_id": 123,
    "type": "invoice",
    "auto_number": true
}

Download PDF

GET /wp-json/polski-pro/v1/invoices/{id}/pdf

Returns a PDF file as application/pdf with a Content-Disposition: attachment header.

Issue correction

POST /wp-json/polski-pro/v1/invoices/{id}/correction

{
    "reason": "Zmiana danych nabywcy",
    "items": [
        {
            "product_id": 45,
            "quantity": 1,
            "net_price": 100.00,
            "vat_rate": 23
        }
    ]
}

Statistics

GET /wp-json/polski-pro/v1/invoices/stats

Returns invoice statistics: total count, net/gross values, breakdown by status.

Hooks

polski_pro/invoices/before_generate

Action fired before generating an invoice.

/**
 * @param int    $order_id ID zamówienia
 * @param string $type     Typ dokumentu (invoice, correction, receipt, packing_slip)
 */
do_action('polski_pro/invoices/before_generate', int $order_id, string $type);

Example:

add_action('polski_pro/invoices/before_generate', function (int $order_id, string $type): void {
    if ($type === 'invoice') {
        // Logowanie generowania faktury
        error_log("Generowanie faktury dla zamówienia #{$order_id}");
    }
}, 10, 2);

polski_pro/invoices/number_format

Filters the invoice number format.

/**
 * @param string $number    Wygenerowany numer faktury
 * @param string $type      Typ dokumentu
 * @param int    $order_id  ID zamówienia
 */
apply_filters('polski_pro/invoices/number_format', string $number, string $type, int $order_id): string;

Example:

add_filter('polski_pro/invoices/number_format', function (string $number, string $type, int $order_id): string {
    if ($type === 'correction') {
        return 'KOR/' . $number;
    }
    return $number;
}, 10, 3);

polski_pro/invoices/pdf_content

Filters the data passed to the PDF template.

/**
 * @param array  $data     Dane faktury (seller, buyer, items, totals)
 * @param int    $invoice_id ID faktury
 */
apply_filters('polski_pro/invoices/pdf_content', array $data, int $invoice_id): array;

Example:

add_filter('polski_pro/invoices/pdf_content', function (array $data, int $invoice_id): array {
    $data['footer_note'] = 'Dziękujemy za zakupy!';
    return $data;
}, 10, 2);

Common issues

PDF generates blank pages

1. Check if the PHP mbstring extension is installed
2. Make sure the wp-content/uploads/polski-pro/invoices/ directory has write permissions (755)
3. Verify that the seller data is filled in the settings

Numbering resets

Numbering resets according to the selected strategy - annual resets on January 1st, monthly on the 1st of each month. If you want continuous numbering, select the “Continuous” strategy.

No VAT on line items

Check the WooCommerce Tax configuration. The plugin retrieves VAT rates from WooCommerce tax settings. Make sure the rates are correctly configured for Poland.

Related resources

• KSeF integration
• Report an issue

This page is for informational purposes only and does not constitute legal advice. Consult a lawyer before implementation. Polski for WooCommerce is open source software (GPLv2) provided without warranty.