How to receive an invoice from Mage2.PRO for an extension purchase?

Thanks for purchase the «SecurePay» Magento 2 extension.
Installation instruction is here: How to install a Mage2.PRO extension?
I have sent the credentials to the email address of your PayPal account.
I have not found the possibility to generate the invoice in PayPal for an already received payment (seems like PayPal allows to generate an invoice only for a future payment, not for an already received one), so I have generated the invoice in an online tool:
Invoice # 2016-10-13-01.pdf (15.0 KB)