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.

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.

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 (AES-256-CBC with HMAC), 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.