Sale not showing

I had a customer purchase a digital product. He went through the checkout process and his money went to my paypal account. But there is no record AT ALL of this happening in the opencart system. It's not recorded in Sales and the download is not added to his account.

Any idea what might cause this?
I realise there could be many factors/variables but hoping someone might be able to shed some light.

Filter your orders by missing orders and see if the order is there. Also check both your OpenCart and PHP error logs.

As AddCreative said, look into the missing orders, they might be in there. Sometimes PayPal fails to call back the OpenCart server (IPN) because of network issues, you can check the latter in your server's raw access log.

Here's a very good article about Missing Orders: https://www.antropy.co.uk/blog/missing-orders/