WHMCS payment module for USDT/USDC blockchain monitoring. Automate invoice payments with stablecoin detection and webhook callbacks via PayzCore.

WHMCS Integration

The PayzCore WHMCS module adds USDT/USDC blockchain monitoring as a payment gateway in your WHMCS installation.

Source: github.com/payzcore/whmcs
Requirements: WHMCS 7.x+, PHP 7.4+, PayzCore account

How It Works

Client views an unpaid invoice and clicks "Pay with USDT/USDC".
WHMCS module calls the PayzCore API.
Payment page shows the wallet address, QR code, and exact amount.
Client sends stablecoins from their wallet.
PayzCore sends a webhook to callback.php.
Module verifies the HMAC signature and applies the payment to the invoice.
Invoice is marked as "Paid".

Installation

Download the module from GitHub releases
Upload the files to your WHMCS installation:

modules/gateways/
├── payzcore.php              ← Main gateway file
└── payzcore/
    ├── callback.php          ← Webhook receiver
    └── lib/
        └── PayzCore.php      ← API client

Also copy the callback file:

modules/gateways/callback/
└── payzcore.php              ← Webhook callback entry point

Set correct file permissions (644 for files, 755 for directories)

Configuration

In WHMCS admin: Setup > Payments > Payment Gateways
Select PayzCore from the dropdown and click Activate
Configure the settings:

Setting	Value	Notes
API Key	`pk_live_...`	From your PayzCore project
Webhook Secret	`whsec_...`	From your PayzCore project
Display Name	"Pay with USDT"	Shown to clients

Click Test Connection. The module calls GET /api/v1/config to auto-detect available chains and tokens from your connected wallet. The chain and token dropdowns are populated automatically — no manual selection is needed.
Set your webhook URL in the PayzCore dashboard to:

https://yourdomain.com/modules/gateways/callback/payzcore.php

Invoice Status Mapping

PayzCore Event	WHMCS Action	Notes
`payment.completed`	Invoice marked as Paid	Payment applied in full
`payment.overpaid`	Invoice marked as Paid	Overpayment amount logged in transaction notes
`payment.partial`	Partial payment applied	Invoice remains unpaid for remaining balance
`payment.expired`	No action	Invoice stays unpaid, client can retry

Overpayment Handling

When a client overpays, the invoice is marked as Paid and the overpayment amount is logged in the WHMCS transaction notes. Refunds or credits must be handled manually by the admin.

If a client sends less than the invoice amount, the received amount is applied as a partial payment. The invoice remains open for the remaining balance. The client can create a new payment for the remainder.

Client Experience

Client views an unpaid invoice in the WHMCS client area
Selects "Pay with USDT" (or your configured display name)
Sees the wallet address, QR code, exact amount, and expiration timer
Sends the exact stablecoin amount from their wallet
Once confirmed, the invoice status updates automatically

Troubleshooting

Gateway not showing in admin

Ensure all files are in the correct directories (see Installation)
Check PHP error logs for syntax errors
Verify file permissions (readable by web server)

Callback not working

Verify the callback URL is accessible from the internet: https://yourdomain.com/modules/gateways/callback/payzcore.php
Check that your server allows POST requests from external IPs
Look for errors in the WHMCS Activity Log: Utilities > Logs > Activity Log

Invoice not updating after payment

Confirm the Webhook Secret matches between PayzCore and WHMCS settings
Check the WHMCS Gateway Log: Utilities > Logs > Gateway Log
Verify the PayzCore webhook delivery status in your PayzCore dashboard

WHMCS