Payment integration with Citrus pay

[Web Architect]

Hi,

We are using Django oscar for our ecommerce platform. I have been working on integrating a payment gateway into the platform. Since, this is the first time with Oscar, I am struggling with the same. This is for Indian market and is an India based payment gateway (Citrus). We are planning to use Citrus based hosted checkout where the users would be directed to Citrus site to select the payment mode and fill in their card/bank credentials. 

I am really not sure where to integrate this - during payment  or during place order submission. The way it would work is that order and merchant details would be in hidden fields in a form in HTML and when the user submits for payment, user would be redirected to the Citrus page where user would enter the payment credentials. On successful/failed payment, Citrus server would send the response back to Oscar platform and users need to be redirected to specific pages accordingly - for successful or failed order. 

The oscar documentation is not elaborate enough to help with the above.

Would appreciate if anyone could direct me with the correct approach regarding the above...

Thanks.