In order to ensure that PayPal calls back your Kartris site, to notify it that a payment for a particular order was made so that confirmation mails can be sent and the order can be tagged as 'paid', you need to set up a few things within your PayPal account.
You may find that orders where data submitted contains non-English characters (such as French or German accented characters) generate an INVALID response at PayPal. To fix this:
We advise doing this even if you're in the US or UK, as it's quite possible you'll have customers with names and/or addresses either domestically or overseas that contain non-English accented characters.
It cannot be done on the callback because that is called by PayPal, not the customer's browser. Unfortunately PayPal puts in a 5-second delay after a completed payment before returning the customer to the store. This inevitably results in some customers dropping out after a successful payment but before they have been redirected back to your site, and hence not being logged by Google Analytics as completed sales. There is no workaround for this; the Google Analytics code can only run on the user's browser; it must run after the payment is complete (otherwise you will log sales as successful that don't complete payment) and PayPal apparently has no way to reduce or eliminate the 5-second delay). This is not a Kartris issue alone; it is an issue with all carts that support Google Analytics when they are set up to use PayPal Web Site Payments Standard.
Ensure your page has the following code pasted near the bottom, before the closing 'body' tag.
Copy this code and place it where you want the help icon to appear in your page.
Your help link will appear as the icon below. Click it to verify how the help content will look.
Place a QR code on your product or machinery to let a user easily retrieve the user guide documentation for it.
Right-click and 'copy'