WHMCS Payment Gateway

Requirements

• A supported WHMCS and PHP installation with PHP cURL enabled.
• A public HTTPS WHMCS System URL that can receive payment callbacks and access the Card2Crypto API.
• A self-custodial USDC Polygon payout wallet. Database permission is needed to create mod_card2crypto on first use; include this table in backups.

Installation

1. Back up the current gateway files and WHMCS database.
2. Extract card2crypto-whmcs-gateway.zip and merge the enclosed modules directory into the WHMCS root beside configuration.php. Include modules/gateways/card2crypto/lib.php and callback.php, together with the gateway and callback modules.
3. Open WHMCS Payment Gateways and activate Smart Card2Crypto Hosted. Card2Crypto Custom is available for a chosen provider; existing direct provider modules can also be retained.
4. Enter USDC Polygon Wallet Address. Keep Custom Domain at pay.card2crypto.org and API Domain at api.card2crypto.org unless dedicated endpoints have been configured. An empty API Domain uses the API default.
5. Review Description and Fees Tolerance, then save changes. In custom mode also check Custom Provider Tag and Minimum Invoice Amount (USD).
6. Pay a staging invoice and confirm it becomes Paid. Review the Gateway Log before relying on automatic service activation.

Recommendations

Use Smart Card2Crypto Hosted as the starting gateway; choose custom or direct modes only for the provider and region you intend to support.

Keep the checkout and API domain settings separate. The API domain does not inherit a custom checkout domain.

Review Fees Tolerance as an amount-acceptance threshold, not a processing fee. Keep amount detection enabled where available and choose the threshold deliberately for your workflow.

For Card2Crypto Custom, select a currently available provider identifier and review Minimum Invoice Amount (USD). Do not rely on the inherited moonpay default. Your configured invoice minimum also applies.

Preserve mod_card2crypto and existing settings in database backups and updates; test a new invoice payment after changes.

Use your own payout wallet
Use a self-custodial 0x wallet you control for USDC payouts on Polygon. Confirm the address and receiving network.

Check provider limits
Set an order or invoice amount above the selected provider’s minimum and allow for fees. Country availability, payment methods and customer verification requirements depend on the provider.

Provider minimums

Reference minimums checked on 27 October 2026. Limits, fees, payment methods and regional availability may change. The selected provider confirms the final amount and any customer verification requirements during checkout.