Yes, you can show your payment form to the customer.
But you will need to confirm these orders manually.
To do this Go to the dashboard and click Payment processing.
Then do the following:
Set the Accept these orders checkbox in the Orders with manual payment processing section.
Enter the URL of your payment form to the Payment page URL.
It will be shown in the iframe immediately after the completion of the order.
If required, specify the payment instruction.
It will be displayed in the order cart.
Specify a appropriate width and height for the form.
Check the result.
There is a payment instruction in the customer's cart.
And after the order was completed, the specified page is shown in the frame.