Just to give you all update on this requirement. In the latest version (21.10.8), there is now Extensions section under Settings tab which allows to inject custom javascript code to various places within Manager.
This is how Manager will handle country-specific requirements to integrate with government and other agencies around the world.
To add QR code to your invoices, follow this guide:
https://www.manager.io/guides/22137
Select Saudi Arabia and then select QR Code to import.
This will simply import extension with the following code.
When sales invoice is viewed, the custom code above will execute which will append QR code at the end of the invoice.
I’m not sure what QR code should encode. Currently I’m just encoding business name but I’m working on making QR code contain all required data, I will improve the script in upcoming days.