What causes a 303 error when I make a call on my website to paypal? Here is a snapshot of the message: http://www.arguemax.com/images/problems/5-21-2014/Capture_02.PNG Watch this new video I made with Ezvid: http://youtu.be/728GYPBLYhU A look at the php code tracks the problem down to this function and "failed with code: {$result[0]} - {$result[1]}" is where the message "failed with code: 303 - rifle" comes from. Can anyone suggest how I can debug this? Code: private function process_request($data) { global $config; $request = new HTTPRequest($this->host, $this->endpoint, 'POST', $config['pp_paypal_secure']); $data['USER'] = $config['pp_paypal'.($config['pp_paypal_use_sandbox'] ? '_sandbox_' : '_').'API_username']; $data['PWD'] = $config['pp_paypal'.($config['pp_paypal_use_sandbox'] ? '_sandbox_' : '_').'API_password']; $data['SIGNATURE'] = $config['pp_paypal'.($config['pp_paypal_use_sandbox'] ? '_sandbox_' : '_').'API_signature']; $temp = http_build_query($data); $result = $request->connect($temp); $return=false; if (is_array($result)) { $this->last_error = "failed with code: {$result[0]} - {$result[1]}"; } elseif ($result<400) { $response = $request->get_content(); parse_str($response, $this->EC_data); // $this->write_results($this->paypal_vars['METHOD'] . ' process request returned = ' . $this->EC_data['ACK']); if ($this->EC_data['ACK'] == 'Success') { $return=true; } else { $this->last_error = 'Failed Validation'; } } else { $this->last_error = "failed with code: {$result}"; } return $return; }