How to show invoicePaymentSuccessAwaitingNotify in viewinvoice.tpl

[Hal9000 12]

The viewinvoice.tpl file shows the $LANG.invoicePaymentSuccessAwaitingNotify string if $paymentSuccessAwaitingNotification is true.
Similarly it does for paymentsuccess, pendingreview etc.

I know the other ones can be triggered by setting a URL parameter. But what is the parameter that sets $paymentSuccessAwaitingNotification to true?
I found it nowhere in the documentation.

[Kian 104]

I could be wrong but I think that it triggers with some gateways when the client returns to the invoice before the callback is complete. In fact the message is the following:

Thank you for completing the payment process. We are awaiting notification to confirm the payment you just made. We will send you an email confirmation as soon as this has been received.

Basically it says «Calm down and don't worry! You have successfully paid the invoice. Just wait few seconds to see the invoice turning to Paid».

[Hal9000 12]

I know, and this is what I want to show. I coded my own gateway module and need to pass the return url to the gateway, but I need to know which parameter to attach to the URL in order to have the message show.

[Hal9000 12]

I just so happened to pay an invoice on whmcs.com via PayPal and I actually got that awaiting notification message.
However the URL shows &paymentsuccess=true and nothing else, so there must be some other criteria that makes that message appear.

Since when adding that variable to viewinvoice.php when the invoice was paid showed the standard paid message, I assume that maybe some variable gets set inside the module_link function if $_GET['paymentsuccess'] is true or something. But which one? Damn...