Official plugin for WHMCS

1. Download the ZIP (or tar.gz) file from the releases See the releases
2. Extract at the root folder of your WHMCS installation. Following files will be copied

├── modules
│   └── gateways
│       ├── callback
│       │   └── khaltigateway.php
│       ├── khaltigateway
│       │   ├── assets
│       │   │   ├── configure_epay.png
│       │   │   └── enable.png
│       │   ├── callback.php
│       │   ├── checkout.php
│       │   ├── init.php
│       │   ├── khalti_helpers.php
│       │   ├── templates
│       │   │   ├── initiate_failed.html
│       │   │   ├── invalid_currency.html
│       │   │   ├── invoice_payment_button.php
│       │   │   └── noninvoice_page.html
│       │   ├── utils.php
│       │   └── whmcs.php
│       └── khaltigateway.php   

(The plugin creates

• file khaltigateway.php under modules/gateways directory of your root installation,
• directory khaltigateway/ under modules/gateways directory of your root installation
• file khaltigateway.php under modules/gateways/callback directory of your root installation. (This file is kept just to maintain the WHMCS convention)

Login to admin area of your WHMCS installation and enable the gateway from Setup -> Payments -> Payment Gateways (Refer to the image below)

Once the gateway is enabled, configure Khalti Payment Gateway with the merchant secrets from admin.khalti.com (Refer to the image below)

PS: Please make sure that the currency "NPR" is selected for the option "Convert to For Processing"