This blog post talks about generating invoice automatically for opencart v 1.5.
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In OpenCart 1.5.1.3, in automated email sent on order, invoice number is not present. It prints a warning instead: “Notice: Undefined variable: invoice_no” To fix it, visit this post: http://forum.opencart.com/viewtopic.php?f=20&t=48733
Qtriangle is now a provider in OpenCart marketplace in India - Blog by Qtriangle Infotech Pvt Ltd