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The WHMCS integration ships as two components that share a single API key:
  • a payment gateway (PawPayments (Crypto)) that pays any WHMCS invoice with crypto,
  • an optional addon (PawPayments Crypto Deposit) that adds an Add Funds page where customers credit their WHMCS balance with crypto.

Download the plugin (.zip)

Ready-to-upload pawpayments-whmcs-<version>.zip (gateway + addon).

View source on GitHub

Source, releases, and issue tracker.
PropertyValue
GitHubpawpayments/whmcs-plugin
DownloadLatest release .zip
WHMCS8.x
PHP7.4+ (8.1+ recommended; WHMCS 8.x supports up to 8.3)
Required extensionscurl, json, mbstring, openssl
DatabaseWhatever WHMCS already uses (MySQL / MariaDB)

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File layout

The release zip mirrors the WHMCS install tree: 
modules/
├── gateways/
│   ├── pawpayments.php                          ← gateway entry point
│   ├── pawpayments/                             ← vendored SDK
│   │   └── vendor/pawpayments/sdk/...
│   └── callback/
│       ├── pawpayments.php                      ← checkout webhook
│       └── pawpayments_topup.php                ← top-up webhook
└── addons/
    └── pawpayments_topup/
        └── pawpayments_topup.php                ← top-up addon (Add Funds)
Drop those folders directly into your WHMCS root, then restore ownership: 
chown -R www-data:www-data \
    modules/gateways/pawpayments.php \
    modules/gateways/pawpayments \
    modules/gateways/callback/pawpayments*.php \
    modules/addons/pawpayments_topup

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Activate the gateway

  1. Setup → Payments → Payment Gateways → All Payment Gateways.
  2. Click PawPayments (Crypto) to activate.
  3. Fill the fields:
    FieldValue
    Display NameCustomer‑facing label, e.g. PawPayments (Crypto).
    API KeyMerchant API key from the Paw dashboard.
    API Base URLhttps://api.pawpayments.com (default).
    Invoice TTL (seconds)Lifetime of the underlying Paw invoice. Default 3600. The same payment_url is reused inside that window.

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Activate the Add Funds addon (optional)

  1. Setup → Addon Modules → PawPayments Crypto Deposit → Activate.
  2. Configure — leave the API Key field empty to inherit the gateway’s key, or enter a separate one.
  3. Grant access to the desired admin roles, save.
The addon creates mod_pawpayments_credits on activation; this small table provides idempotency for the top‑up webhook (primary key on order_id). The customer top‑up page is then available at https://<your-whmcs>/index.php?m=pawpayments_topup. Link to it from a custom client‑area menu item.

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Webhook URLs

The plugin sends notify_url on every invoice it creates, so manual webhook setup is not required. The endpoints are:
PurposeURL
Checkouthttps://<your-whmcs>/modules/gateways/callback/pawpayments.php
Top‑uphttps://<your-whmcs>/modules/gateways/callback/pawpayments_topup.php
If the merchant account requires a default webhook URL, use the checkout one. Both endpoints must be reachable over HTTPS.

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Lifecycle

Checkout. addInvoicePayment is called with the Paw order_id as transactionId, so duplicate webhook deliveries never double‑pay an invoice. Top‑up. Each top‑up creates a one‑shot Paw invoice via POST /api/v2/invoices and is recorded in mod_pawpayments_credits keyed by order_id. On webhook success the WHMCS AddCredit API is called, visible on Clients → Client Profile → Summary → Credit Balance. Webhooks carrying a permanent_address_id are silently acknowledged with 200 OK.

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Smoke test (checkout)

ORDER_ID="<paw_order_id>"
INVOICE_ID="<whmcs_invoice_id>"
KEY="<your_api_key>"
BODY="{\"order_id\":\"$ORDER_ID\",\"extra\":\"$INVOICE_ID\",\"status\":\"success\",\"fiat_amount\":\"15\",\"asset\":\"USDT\"}"
SIG=$(printf '%s' "$BODY" | openssl dgst -sha256 -hmac "$KEY" | awk '{print $2}')

curl -X POST "https://<your-whmcs>/modules/gateways/callback/pawpayments.php" \
  -H "Content-Type: application/json" \
  -H "X-Paw-Signature: $SIG" \
  -d "$BODY"
Expected: OK with HTTP 200, and the WHMCS invoice transitions to Paid.

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Troubleshooting

SymptomCause / Fix
Gateway not in the list at Setup → Payments → Payment GatewaysFiles not uploaded or wrong path. Verify modules/gateways/pawpayments.php exists and is readable by the web user.
Failed to create payment: Invalid API keyAPI key wrong or merchant not activated.
Webhook returns HTTP 500 with Failed to open required init.phpOutdated callback. Current callback uses require_once __DIR__ . '/../../../init.php'; (three .., not four). Re‑upload the latest callback/pawpayments*.php.
Webhook returns HTTP 401 Invalid signatureThe API key in gateway settings does not match the one used to issue the invoice. Update settings and re‑issue.
Top‑up addon not visibleActivate it under Setup → Addon Modules and grant access to your admin role.
Module Not Activated on top‑upThe gateway must be enabled — the addon falls back to the gateway’s API key.
Duplicate top‑upsmod_pawpayments_credits prevents this. If the table is missing, re‑activate the addon.
WHMCS gateway logs are at Utilities → Logs → Gateway Log (filter by pawpayments).

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Uninstall

cd /path/to/whmcs
rm -rf modules/gateways/pawpayments.php \
       modules/gateways/pawpayments \
       modules/gateways/callback/pawpayments.php \
       modules/gateways/callback/pawpayments_topup.php \
       modules/addons/pawpayments_topup
Deactivate the addon and gateway from the WHMCS admin first. Optionally drop the bookkeeping table: 
DROP TABLE IF EXISTS mod_pawpayments_credits;