Interkassa — Payment Processing for OpenCart 2.3, 3 and 4

Interkassa for OpenCart is a payment module that accepts payments through the Interkassa aggregator: the shopper pays on the secure sci.interkassa.com page (card, payment systems, terminals — whatever is enabled in your cashbox), and the result comes back to the shop as a signed server callback. The module verifies the signature, the cashbox ID and the amount — and sets the correct order status itself, with no manual reconciliation against the dashboard.

The package includes three builds — a native one for OpenCart 4.0.2–4.1.x and separate ports for OpenCart 3.0.2–3.0.5.0 and 2.3.0.x. Accepting payments is in the free version. The Pro key adds a payment log with Interkassa statuses, invoice numbers, and reconciliation against orders.

What the admin gets

How it works, step by step

1. At checkout, the shopper chooses “Online payment (Interkassa)” and confirms the order.
2. The module builds a signed SCI form (amount, currency, payment number, four return URLs) and sends the shopper to the Interkassa payment page.
3. Interkassa processes the payment and sends the shop a callback to the interaction address (ik_ia_u).
4. The module verifies the signature (md5 or sha256 — as configured in the cashbox), the cashbox ID and the amount. A request that doesn’t match on even one of these is rejected with a 403.
5. The order gets a status — “paid”, “declined” or “awaiting payment” — according to your status map, and a repeated identical callback doesn’t add a second entry to the history.
6. With Pro, every payment lands in the log: Interkassa status, amount, invoice number, authorisation code, and a test-mode flag.

Price

1,490 UAH — a one-off purchase. The licence is perpetual: you pay once, and updates and technical support are included in the price. One key covers one domain and its subdomains.

Moving the shop to another domain — deactivate the licence on the old one and activate it on the new one yourself in the dashboard.

The licence is perpetual — nothing expires or switches off. One key covers one domain; moving the shop means deactivating the licence on the old domain and activating it on the new one yourself.

One key covers one domain. Moving the shop means deactivating the licence on the old domain and activating it on the new one yourself, with no need to contact support.

Trial first, payment later. A fresh install is a plain free version: nothing Pro switches on by itself. When you want to see Pro in action, click “Try Pro” in the module’s settings and enter your email — a 7-day key arrives straight into the modal and is also sent by email. The payment log can be checked on your own shop before you buy. That’s exactly why refunds after payment aren’t offered — you see the module working before you pay.

Technical requirements

• OpenCart 4.0.2 – 4.1.x (native build), 3.0.2 – 3.0.5.0 or 2.3.0.x (separate ports)
• PHP 8.0+ for OpenCart 4, 7.x for OpenCart 3, 5.6–7.0 for OpenCart 2.3
• Cashbox ID and secret key from the Interkassa dashboard — needed only for live mode

Under the hood

• Native code for OpenCart 4 — namespaces, Twig, the standard installer; for OpenCart 3 and 2.3, separate ports are built rather than one “works on every version” archive.
• The secret key is stored encrypted, tied to the installation — a database dump won’t contain it in plain text.
• A callback without a valid signature is rejected, as is a request with the wrong cashbox ID or a different amount — an order’s status can’t be changed by a third-party request.
• A paid order isn’t rolled back: a late or forged callback with status “declined” doesn’t overwrite either the order or the log, and the shopper returning via the “Back” button doesn’t create a second payment on the same order.
• A soft Pro gate: the log is always visible, but without a key the button is greyed out — it’s immediately clear what the licence unlocks. Once the trial ends, only the log switches off; payment acceptance doesn’t stop.

How to install

1. Extensions → Installer: upload interkassa.ocmod.zip. For OpenCart 3.0.x, take interkassa-oc3.ocmod.zip from the product’s downloads.
2. OpenCart 2.3: take interkassa-oc2.ocmod.zip and upload the contents of the upload/ folder to the shop’s root via FTP/SFTP or a hosting file manager — the standard 2.3 Installer only copies files over FTP and fails on most hosting with “FTP needs to be enabled in the settings”. Then go to Extensions → Payments → Interkassa → “+”.
3. In Extensions → Payments, find Interkassa and click “Install”, then open its settings.
4. Enable the module, enter the cashbox ID and secret key, and choose the signature algorithm — the same one set in your Interkassa cashbox settings.
5. Copy the “Interaction URL” from the module’s settings and set it in the Interkassa dashboard as ik_ia_u.
6. For the first check, leave test mode on — payment goes through the test gateway, no real funds are taken.
7. For Pro: click “Try Pro”, or paste the licence key from the email after purchase — the log appears immediately, with no reinstall needed.

Version history

1.1.1 — 14 August 2026

Added a build for OpenCart 2.3.0.x (.tpl templates, settings without the payment_ prefix, the admin’s token token) — the same Free/Pro model and the same licence key. Fixed in the 2.3 and 3.x builds: a callback whose amount doesn’t match the order no longer rolls an already-paid order back to “awaiting payment” — after a successful payment, the next callback is simply acknowledged and changes nothing. Amount verification for unpaid orders still works as before.

1.1.0 — 14 August 2026

Rebuilt the Free/Pro model: a fresh install no longer switches on Pro by itself — the 7-day trial is only issued by clicking “Try Pro”, arriving as a key in the modal and by email. The licence is checked against the CatCode server with a daily cache and a 14-day grace period. The payment log stays in place, but is greyed out without a key, with a Pro badge. Fixed: a late or forged callback with status “declined” no longer overwrites the log of an already-paid order; returning via the “Back” button no longer creates a second payment on top of a paid order or loses the invoice number.

1.0.0 — July 2026

First release: payment via Interkassa SCI, a signed server callback with md5/sha256 verification, cashbox ID and amount reconciliation, IP whitelist, test mode, status map, logging; Pro — payment log. Builds for OpenCart 4.0.2–4.1.x and 3.0.2–3.0.5.0.