Quick subscribe in iBox popup

Hi,

I have an iBox popup for ‘subscribe’ where the quick subscribe plugin comes up with just a textbox and button.
When a user subscribes it loads the index page but does not subscribe the user.

Could anyone give me a step-by-step for doing it properly.
I would love for the user to be taken to another iBox ‘thank you’ popup once they have subscribed or for it to even load using ajax in the same popup.

I’d appreciate any help. Thank you