Installment Payment Development on 1C-Bitrix

Installment Payment Development on 1C-Bitrix: from Bank Widget to Custom Module

Customers are increasingly abandoning purchases if there is no installment option. Standard Bitrix tools do not provide this functionality — we have to develop a custom module or integrate a bank widget. We offer both options: from a quick embed of Tinkoff or Halva to a full-fledged system with flexible scheduling and overdue control. In this article — architecture, typical code, and practical recommendations for a developer.

Typical development pain points: incorrect rounding of payments, lack of synchronization with 1C via CommerceML, overdue without notifications. We address each with proven solutions. For example, rounding is corrected by moving pennies to the last payment — precise math without losses. After implementing installment, purchase conversion increases by 15-25%, and average order value increases by 30%. Our solutions have been load-tested on catalogs up to 200,000 products — the system operates steadily under peak loads.

How to develop installment payment functionality on 1C-Bitrix?

Let's compare two approaches. A bank widget (3-5 days) is suitable for a quick start and does not require complex accounting. A custom installment system (8-12 days) is for stores with a turnover of 10 million RUB/month or more, where bank commissions (often 5-7%) become significant. A custom system pays for itself in 2-3 months due to zero commissions. Savings on commissions can reach 7% of turnover — for a turnover of 10 million RUB, that's hundreds of thousands per year.

How to integrate bank installment?

Consider integration with Tinkoff Installment (Dolyami service). The bank provides a JavaScript widget that is embedded into the product card. After payment, the bank sends a webhook with the result.

Example code for handling the webhook in PHP:

$input = json_decode(file_get_contents('php://input'), true);
if ($input['status'] === 'approved') {
    $orderId = (int)$input['orderReference'];
    $loanId = (int)$input['loanId'];
    \Bitrix\Sale\Order::load($orderId)->setField('STATUS_ID', 'PAID')->save();
}

The integration process includes:

1. Place the button on the product card using the JavaScript widget.
2. Upon successful bank response, create an order via \Bitrix\Sale\Order::create(), attach the payment system, and save the loan_id from the bank in the order property.
3. Configure processing of the webhook from the bank to update the order status.

What is a custom installment system and how to implement it?

A custom installment system does not require a bank — the store itself splits the amount into parts. Two tables are needed to store data.

Table b_local_installment_plan:

Table b_local_installment_payment — payment schedule:

How to calculate the payment schedule?

function createInstallmentSchedule(int $planId, float $totalAmount, float $downPayment, int $installmentsCount): void
{
    $remainingAmount = $totalAmount - $downPayment;
    $installmentAmount = round($remainingAmount / $installmentsCount, 2);

    // Correct rounding on the last payment
    $lastPaymentAmount = $remainingAmount - ($installmentAmount * ($installmentsCount - 1));

    for ($i = 1; $i <= $installmentsCount; $i++) {
        $dueDate = (new DateTime())->modify('+' . ($i * 30) . ' days');
        InstallmentPaymentTable::add([
            'PLAN_ID' => $planId,
            'PAYMENT_NUMBER' => $i,
            'DUE_DATE' => $dueDate,
            'AMOUNT' => ($i === $installmentsCount) ? $lastPaymentAmount : $installmentAmount,
            'STATUS' => 'PENDING',
        ]);
    }
}

Display in product card and cart

On the product page, we show a block with terms:

Price: [individually calculated]
Installment for 6 months:
├── Down payment: [first installment amount]
└── 5 payments of [monthly amount] every 30 days

Dynamic calculation when selecting the number of months — via AJAX. The endpoint calculates the down payment (20%) and the monthly payment amount, returns JSON.

Payment control and overdue

An agent or cron checks overdue payments daily:

$overdue = InstallmentPaymentTable::getList([
    'filter' => ['STATUS' => 'PENDING', '<DUE_DATE' => new DateTime()],
])->fetchAll();

foreach ($overdue as $payment) {
    InstallmentPaymentTable::update($payment['ID'], ['STATUS' => 'OVERDUE']);
    // Notify the customer
    sendOverdueNotification($payment);
    // If overdue > 30 days — escalate to manager
}

Customer personal account

The page /personal/installments/ shows:

• Active installment plans with payment progress.
• Schedule of upcoming payments.
• History of paid installments.
• Link to pay the nearest payment.

What is included in the work (deliverables)

• Technical specification and architectural documentation.
• Module source code with comments.
• Administrator's operation manual.
• Manager training on installment management (30 min).
• 2 weeks of technical support after launch.
• Load testing on your catalog.

Development timeline

Advantages of working with us

We are certified 1C-Bitrix partners with extensive experience. Our solutions have been load-tested on catalogs up to 200,000 products. Average integration time — 4 days. Purchase conversion increases by 15-25% after installing installment. A bank widget is 3 times faster to implement, but a custom system provides full control over funds.

According to CommerceML documentation, this is the standard for data exchange with 1C. Our modules correctly synchronize payments and installment statuses via this protocol.

Request a consultation about installment payment implementation today. Write to us — we will evaluate your project within one business day. We have completed over 50 installment projects, and the average integration time is 4 days. Contact us to discuss your project.

1C-Bitrix Module Development and Setup

The main trap of Bitrix is init.php. You add an OnBeforeIBlockElementUpdate handler there, then another one — a year later the file is 2000 lines, and on every hit all that code executes. We move business logic into full-fledged modules with D7 ORM, custom tables, and administrative interface. The module can be disabled, transferred to another project, covered with tests — none of that is possible with init.php. Our team has 10+ years of Bitrix experience, certified specialists, and a 6-month code guarantee. Request a consultation — we'll explain how to migrate legacy code to a modular architecture.

Why is init.php the worst place for business logic?

Init.php does not support class autoloading, lacks an isolated namespace, cannot be unit tested, and cannot be disabled without editing the file itself. Every handler written there runs on every request, even if not needed. In a module, you register handlers through EventManager, and they only execute when the event occurs. Performance difference: up to 3x with 10+ handlers.

Standard Modules: Typical Problems and Solutions

Information blocks. IBlock architecture is the first thing we review on any project. A classic mistake: one catalog infoblock with 80 properties, 30 of which are multiple. The b_iblock_element_property table swells to millions of rows, and CIBlockElement::GetList with filtering on three properties does a full scan. We move reference data to Highload-blocks, eliminate multiple properties where possible, and design the structure for 5x growth.

e-Store (sale). Cart business rules are a separate story. We set discount priorities to prevent two campaigns from giving 60% instead of 30%, connect payment handlers, and write custom validation via OnSaleOrderBeforeSaved.

Search. The built-in search module with morphology works up to 10–15 thousand elements. Beyond that — Elasticsearch. We configure it via the Bitrix search module API, indexing through CSearchFullText or custom indexers.

Highload-blocks for dictionaries, logs, user data — instead of bloated IBlocks. Direct queries via Bitrix\Highloadblock\HighloadBlockTable, custom tables instead of the EAV structure of standard infoblocks. A million records — no degradation.

Mail events. Configuration is not just templates in b_event_message. The key is SPF, DKIM, DMARC on the DNS, otherwise transactional emails go to spam. We check deliverability and set up bounce handling.

How to Design Infoblocks for Performance?

We use Highload-blocks for reference data (colors, sizes, manufacturers) that are not involved in complex queries. For SKUs — a separate infoblock with linking via IBLOCK_ELEMENT_PROPERTY. Enable INDEX_PROPERTY for frequently filtered properties. Tagged caching: when an element changes, only the related cache is cleared. Highload-blocks process up to 10x faster than infoblocks with multiple properties on volumes of 100,000 records.

Custom Module Development

Each module follows the structure /local/modules/vendor.modulename/:

• install/index.php — setup class, create tables via $DB->RunSQLBatch()
• lib/ — D7 ORM classes, extending Bitrix\Main\ORM\Data\DataManager
• admin/ — administrative pages using CAdminList, CAdminForm
• include.php — autoloading, event handler registration via EventManager::getInstance()->registerEventHandler()
• REST API endpoints via \Bitrix\Rest\RestManager

The module registers in the system, appears in the "Installed Solutions" list, and has its own settings at /bitrix/admin/settings.php?mid=vendor.modulename. It can be enabled, disabled, and updated through UpdateSystem or custom migration mechanics.

Examples of implemented tasks:

• Campaign management — visual condition builder via CAdminCalendar, timers via agents (CAgent::AddAgent), analytics linked to the sale module
• Cost calculator — React widget on the frontend, REST API in the module, formulas stored in a Highload-block
• Booking system — real-time calendar, locking via $DB->StartTransaction() / $DB->Commit() on concurrent requests, integration with channel manager via webhook

Components and Composite Cache

Component customization via result_modifier.php and component_epilog.php, not by editing template.php of the standard template. This way core updates are painless.

Composite cache ("Composite Site" technology) — the server sends ready HTML, bypassing PHP routing. Dynamic areas (cart, authorization) are loaded via CBitrixComponent::setFrameMode(true) and AJAX. TTFB drops to 30–50 ms. But there are caveats: not all components are compatible, $APPLICATION->ShowPanel() breaks composite, and careful markup of <div id="bx-composite-..."> is required.

What to Check Before Installing a Marketplace Module?

Before installing a module from the marketplace, an audit is mandatory. We check: SQL queries without prepared statements (hello SQL injection), direct use of $_REQUEST without filtering, use of outdated kernel API instead of D7, conflicts with the composite cache module. A module with no updates for over a year and a few dozen installations is likely a problem on the next PHP update. A typical case: a module calls CIBlockElement::GetList with no cache reset — the site crashes with 5000 elements.

Migration to D7

When upgrading PHP or switching to a new edition — refactor outdated calls:

• CIBlockElement::GetList() → Bitrix\Iblock\Elements\ElementTable::getList()
• CSaleOrder::GetList() → Bitrix\Sale\Order::getList()
• CModule::IncludeModule() → Bitrix\Main\Loader::includeModule() Testing on staging, rollback via git on issues.

According to official 1C-Bitrix documentation, D7 ORM is the recommended tool for working with data, providing type safety and automatic query generation.

Comparison: Init.php vs Module

Module Development Scope and Cost

What is included in module development?

• Technical specification and architectural plan
• Code following PSR-4 and Bitrix code style
• Unit tests (PHPUnit) for business logic
• Integration tests for events and REST API
• Installation, configuration, and API documentation
• Repository and documentation access
• Administrator training for module usage
• 6-month warranty support

Estimated timelines and complexity:

Cost is calculated individually — contact us for a project estimate.

Module Testing

Unit tests via PHPUnit cover business logic: discount calculation, validation, document generation. Mocks for Bitrix\Main\Application::getConnection() allow tests to be DB-independent. Integration tests verify event handlers on a real database — OnAfterIBlockElementAdd, OnSaleOrderSaved, etc. REST API endpoints are tested via curl or PHPUnit HTTP client. Critical for modules working with b_sale_order, b_catalog_price — where errors cost money.

Compatibility is checked on PHP 7.4, 8.0, 8.1, 8.2 and editions: Standard, Small Business, Business. We check conflicts with popular marketplace modules — they often intercept the same events. Load testing: measurements on 10K, 100K, 1M records, profiling via Xdebug for memory leaks and N+1 queries.

Practical Examples

Campaign module for an electronics chain. The built-in sale module discounts did not cover scenarios like "2+1", a gift with purchase over a certain amount, or combined conditions. We built a visual builder: marketers create rules via drag-and-drop without development tickets. Campaign calendar, auto-deactivation via agents, analytics linked to b_sale_order — conversion, average check, usage count. Time to launch a new campaign dropped from two days to half an hour.

Calculator for builders. Parameters (area, materials, number of floors) → formula → preliminary estimate → lead to CRM via CRest::call('crm.lead.add'). Regional coefficients and seasonal markups from a Highload-block, material prices from 1C exchange. The number of target leads increased by a third: clients see a breakdown before calling a manager.

Booking for a hotel chain. Real-time availability via AJAX requests to a custom table vendor_booking_slots, seasonal tariff calculation, synchronization with Booking.com via channel manager API. Room locking on concurrent booking via SELECT ... FOR UPDATE in transactions. Timezones handled via \DateTimeZone — a guest from Vladivostok and a manager from Moscow see the same picture.

We will evaluate your project within one day. Write to us — we'll tell you what is included in turnkey development. Contact us for a consultation on your project. Order a custom module development — get a ready solution with documentation and support.