Guest link pay now button shows a blank page

SOLVED: I had to install CURL on the server and use the PayPal sandbox test account to test the payments. Everything works fine now. There should be a check to make sure curl is installed because the error logs do not say anything about that.

I am using version 1.4.2. I’m trying to get the Merchant Account payment system working. I have entered all the required PayPal information and set it to test mode. When I go to the guest link of an unpaid invoice and click the Pay Now button a blank white page loads and nothing else happens. This is all I get in the logs:

DEBUG - 2015-06-19 16:11:36 --> Config Class Initialized
DEBUG - 2015-06-19 16:11:36 --> Hooks Class Initialized
DEBUG - 2015-06-19 16:11:36 --> Utf8 Class Initialized
DEBUG - 2015-06-19 16:11:36 --> UTF-8 Support Enabled
DEBUG - 2015-06-19 16:11:36 --> URI Class Initialized
DEBUG - 2015-06-19 16:11:36 --> Router Class Initialized
DEBUG - 2015-06-19 16:11:36 --> Output Class Initialized
DEBUG - 2015-06-19 16:11:36 --> Security Class Initialized
DEBUG - 2015-06-19 16:11:36 --> Input Class Initialized
DEBUG - 2015-06-19 16:11:36 --> XSS Filtering completed
DEBUG - 2015-06-19 16:11:36 --> XSS Filtering completed
DEBUG - 2015-06-19 16:11:36 --> Global POST and COOKIE data sanitized
DEBUG - 2015-06-19 16:11:36 --> Language Class Initialized
DEBUG - 2015-06-19 16:11:36 --> Language Class Initialized
DEBUG - 2015-06-19 16:11:36 --> Config Class Initialized
DEBUG - 2015-06-19 16:11:36 --> Loader Class Initialized
DEBUG - 2015-06-19 16:11:36 --> Controller Class Initialized
DEBUG - 2015-06-19 16:11:36 --> Payment_Handler MX_Controller Initialized
DEBUG - 2015-06-19 16:11:36 --> Config file loaded: application/config/invoice_plane.php
DEBUG - 2015-06-19 16:11:36 --> Session Class Initialized
DEBUG - 2015-06-19 16:11:36 --> Helper loaded: string_helper
DEBUG - 2015-06-19 16:11:36 --> Session routines successfully run
DEBUG - 2015-06-19 16:11:36 --> Helper loaded: url_helper
DEBUG - 2015-06-19 16:11:36 --> Database Driver Class Initialized
ERROR - 2015-06-19 16:11:36 --> Severity: 8192  --> mysql_pconnect(): The mysql extension is deprecated and will be removed in the future: use mysqli or PDO instead /var/www/html/inv/system/database/drivers/mysql/mysql_driver.php 92
DEBUG - 2015-06-19 16:11:36 --> Helper loaded: form_helper
DEBUG - 2015-06-19 16:11:36 --> Form Validation Class Initialized
DEBUG - 2015-06-19 16:11:36 --> Helper loaded: number_helper
DEBUG - 2015-06-19 16:11:36 --> Helper loaded: pager_helper
DEBUG - 2015-06-19 16:11:36 --> Helper loaded: invoice_helper
DEBUG - 2015-06-19 16:11:36 --> Helper loaded: date_helper
DEBUG - 2015-06-19 16:11:36 --> Helper loaded: redirect_helper
DEBUG - 2015-06-19 16:11:36 --> Model Class Initialized
DEBUG - 2015-06-19 16:11:36 --> File loaded: application/modules/settings/models/mdl_settings.php
DEBUG - 2015-06-19 16:11:36 --> Model Class Initialized
DEBUG - 2015-06-19 16:11:36 --> Language file loaded: language/english/ip_lang.php
DEBUG - 2015-06-19 16:11:36 --> Language file loaded: language/english/form_validation_lang.php
DEBUG - 2015-06-19 16:11:36 --> Language file loaded: language/english/custom_lang.php
DEBUG - 2015-06-19 16:11:36 --> Helper loaded: language_helper
DEBUG - 2015-06-19 16:11:36 --> File loaded: application/controllers/../modules/layout/controllers/layout.php
DEBUG - 2015-06-19 16:11:36 --> Layout MX_Controller Initialized
DEBUG - 2015-06-19 16:11:36 --> Encrypt Class Initialized
DEBUG - 2015-06-19 16:11:36 --> File loaded: application/modules/invoices/models/mdl_invoices.php
DEBUG - 2015-06-19 16:11:36 --> Model Class Initialized

Is this a bug? There doesn’t seem to be anything in the logs that can describe why I am getting a blank page. Any help would be appreciated.

ADDITION: When the button Pay Now button is clicked a 500 Internal Server Error is returned. What log files can I check for this? I checked Apache logs but there is nothing relevant.

ADDITION #2: Further debuging shows it’s failing at this line “$response = $this->merchant->purchase($params);” in payment_handler.php . Not sure why… yet.

ADDITION #3: Turns out I needed to install CURL on the server. When I did that I now get the error “Security header is not valid”