Android - Google Wallet API - Insert a Pass to the Google Wallet without using server side

Question

is it possible to insert a pass to Google Wallet without calling a custom API? I want to insert a membership card (EAN code with some informations)

I found this: https://developers.google.com/wallet/generic/android

There is a method:

walletClient.savePasses(newObjectJson, this, addToGoogleWalletRequestCode)

But I'm not sure how to get newObjectJson.

Also before that there is

  "id": "ISSUER_ID.OBJECT_ID",
  "classId": "CLASS_ID",
  "iss": "OWNER_EMAIL_ADDRESS",

But I don't where I can get OBJECT_ID. It should be somewhere in Google Wallet API (https://pay.google.com/business/console/) right? A see there Issuer ID and Class ID (its name of the class that I created in that console). And what should exactly be OWNER_EMAIL_ADDRESS?

Is there a full example of that JSON which I can pass to savePasses() method? Or some good tutorial about it?

Or I have to build a custom API for that?