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Troubleshooting

Payment Fails or Order Stays "Pending"​

Cause: The most common cause is a misconfigured or unreachable callback URL.

Fix:

  1. Go to WordPress Admin > MMG Checkout Control Panel > Dashboard tab.
  2. Copy the Callback URL shown there.
  3. Log in to your MMG merchant portal and paste this URL into the callback/webhook field.
  4. Ensure your site has a valid SSL certificate — MMG requires HTTPS to deliver callbacks.
  5. If using sandbox mode, register the callback URL in the MMG sandbox portal, not the live portal.

Plugin Not Appearing in WooCommerce Payment Methods​

Cause: Plugin is inactive, or WooCommerce is not installed and active.

Fix:

  1. Go to WordPress Admin > Plugins and confirm both WooCommerce and MMG Checkout show status "Active".
  2. Go to WooCommerce > Settings > Payments. If MMG Checkout appears, toggle it on and save.
  3. If it still doesn't appear, deactivate and reactivate the MMG Checkout plugin.
  4. Check for plugin conflicts by temporarily deactivating other plugins and testing again.

Callback URL Not Being Received​

Cause: A firewall, caching plugin, or server config is blocking POST requests to the callback endpoint.

Fix:

  1. Confirm your server allows incoming POST requests from MMG's servers.
  2. If you use a caching plugin (W3 Total Cache, WP Super Cache, LiteSpeed Cache), exclude your callback URL from caching rules.
  3. Go to MMG Checkout Control Panel > Logs tab and check for 403 or 500 errors on incoming callbacks.
  4. Check with your hosting provider or WAF administrator to whitelist POST requests to your callback URL endpoint.

Wrong Credentials Error​

Cause: Keys entered incorrectly, or Live credentials used in Sandbox mode (or vice versa).

Fix:

  1. Go to MMG Checkout Control Panel > Credentials tab.
  2. Confirm you are using the correct credential set for the current mode (Sandbox vs. Live).
  3. Re-copy credentials from the MMG merchant portal — do not type them manually.
  4. Ensure there are no leading or trailing spaces in the credential input fields.

SSL Certificate Error​

Cause: Missing or invalid SSL certificate on your WordPress site.

Fix:

  1. Confirm your site URL begins with https:// in WordPress Admin > Settings > General.
  2. Install a valid SSL certificate. Free certificates are available via Let's Encrypt.

Order Status Not Updating After Payment​

Cause: The MMG callback was not received or was processed with an error.

Fix:

  1. Go to MMG Checkout Control Panel > Logs tab and look for callback errors on the relevant transaction.
  2. In WooCommerce > Orders, open the order and check the order notes section for MMG payment events.
  3. If the transaction shows as completed in the MMG merchant portal but the WooCommerce order is still pending, contact MMG Merchant Support with the transaction reference number.

Getting Support​

For issues not resolved by this guide, contact MMG Merchant Support with:

  • Your MMG merchant ID
  • The transaction reference number (if applicable)
  • The error message or log entry from the Logs tab
  • Your WordPress and WooCommerce version numbers

See System Requirements for version compatibility information.