I am new to integrate Google Wallet and there are some confusion and questions related to that given below:
Anyone have idea about this. Thanks in advance.
Can you clarify which specific API (Instant Buy or Wallet for Digital)?
Is it possible to add multiple items...
Digital - no, you can however "bundle", see this post for clarification.
Instant Buy - it's just a "layer" on top of your (pre) existing purchase/ordering processes and handles (just) the payment data of a Google Wallet user. The "order details" is something you control. See sample of data you send.
Discounts by API
By API - no. You can pass whatever (pre-calculated) value in both APIs.
Success vs. Failure Postback
Digital - Google will only send HTTP Post to your server URL on successful transaction. See #5: "Google sends an HTTP POST message to the postback URL whenever a purchase completes..."
Instant Buy - not relevant. You are processing the transaction, unlike in Digital where Google is. Instant Buy in a nutshell provides your web site, secure access to a Google Wallet user's data. You need to have your own merchant account/processor, be PCI compliant, etc. That said, you will have the success or failure info that you actually have to send to Google - they need to know if you have successfully processed or not (yup, it's the other way around).
Refund by API
By API - Unless a Googler says otherwise, AFAIK, not at this time, for both APIs.
On that note, for Instant Buy, it's actually unclear to me how to "inform Google" when performing a credit or refund. Its still a "private API" (not GA) so I actually haven't seen its "guts". It's understood that since the merchant uses their own processor that a credit/refund is the same procedure, but letting Google "know" about it (days/weeks after the fact) is something I personally have no actual info on..sorry...I can assume some "button" in merchant center for Instant Buy, but that's just a guess....
Hth....
