KetchRescue - Thank you very much for the updated API. If you ever get around to updating it again, please note that certain ciphers are no longer supported and after 16 hours of downtime and many emails back and forth with PnP their support team helped me make some code changes:

Approx line 440 - remove "--cipher rsa_rc4_128_sha" from "exec("$curl_path --cipher rsa_rc4_128_sha -d \"$data\" https://pay1.plugnpay.com/payment/pnpremote.cgi", $response);"

Approx line 450 - comment out "curl_setopt($ch, CURLOPT_SSL_CIPHER_LIST, "rsa_rc4_128_sha"); //CentOS 6 Compatibility"

My site was brought to a standstill because using those ciphers caused Error 99: Empty cURL reponse. It's great to be back up and running and your API is fantastic!