If the system is installed correctly and you see the main page without a problem; but when you try to send an order you see a 500 Error; this is due to mail problems.

Please login to your admin panel with the default login information and go to Settings -> Mail Settings and change the settings. If you decide not using mail system, you can disable it from the Notification panel.

After you disable it; system will give an error message when a customer places an order; the error message contains your email address so they can notify you with the order.
Contents of this message can be changed from language files. Please refer to the related docs.

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