osCommerce v2.3.1 and SagePay Direct: Error 4020: Invalid IP Address

Two possible error messages for 4020: “Information received from an Invalid IP address” and just “Invalid IP address”. While I was configuring SagePay Direct for an osCommerce store I made, the checkout process wasn’t completing because SagePay was returning error 4020. This means that the IP address I added to the “Valid IPs” tab on

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