page for external payment processor after order placed

[thorn4life]

Hi Prestations, 

i'm trying to find a solution for a plugin that we are building for presta. 
We need a step in between the "order placed" and "order processed" 
At that time there should be a QR Code visible, which can be used by an app to start the payment process. 
While the QR Code is visible a callback should check if the payment has been made and afterwards jump to the processed page. 

Is there maybe a known plugin that works already in this way? 
We couldn't figure out a nice way to handle this - i searched in the forum but also couldn't find something which leads in this direction

Best Regards,
Roman