Hello,
I will try to explain
1. I have asked to take care of billing address because for Income Tax computation, the billing address is important. If it is delivered in your name as billing, you have officially bought that item for yourself. You have to always mention the final consumer name and address in billing too. Flipkart has no issue as it considers shipping address itself as billing everytime, but amazon will have 2 address billing and shipping. In general hy default, your most used address for deliveries will be taken as billing - which you have change manually while placing the order.
2. The problem I faced is not because of bank offer. There were 2 items in 1 order, 1 is delivered but other phone is cancelled by flipkart. Once the phone is marked out for delivered by you, there is no option to cancel it in Yaper. So, i cannot cancel it, the deliver will not happen, yaper order is not completed - money will not be processed to my account for the delivered phone as well. I had to speak with customer care and explain, it took me 2 weeks to get this resolved and get my payment for the 1st delivered phone.
In your case, if you loose the bank offer because 1 product is cancelled - then if you have any slight chance cancel the other item in the order also before it gets delivered. Because Yaper will not provide you extra amount than what was was promised for that single item, so you will end up paying the discount you have got on the order.
If the other product is already delivered, then it is tough for you - as you have to contact Yaper Support to get that extra amount. Yaper will take amount from end customer after deducting the discount - hence the loss will be eventually borne by Yaper - takes a lot of time and effort from you to get it resolved
Now a days, I noticed that they have closed telegram channel and removed individual contact numbers for customer support. So you have to raise the issue inside app and it is not going to be immediate response. I suggest to be careful, especially with Flipkart as they will cancel the order sometimes - never faced it with Amazon