You can bundle products/items, but you can't use the same ID with different items.
Perhaps if you explained why you need such a scheme someone can make suggestions.
It's unclear exactly what you are suggesting - but there are two types of IAPs, consumables and non-consumables, and each IAP has its own productId. A user can purchase a non-consumable IAP only in quantity 1. Any repurchase of that same non-consumable would be 'for free' and would represent only restoring the original purchase. A user can purchase a consumable IAP in any quantity and multiple times. So perhaps the answer to your 'question' is simply 'use a consumable IAP'. A more precise answer to the question -
'How can I let a user purchase from a large inventory of products'
'Use a few consumable IAPs called CREDITS and sell them as individual products in packages of, for example, 1 CREDIT and 5 CREDITS and 10 CREDITS. After purchasing, for example, 2 '10 CREDITS' allow the user to select 20 different items from the inventory and each time they select a product, debit their account one CREDIT and credit them with that item from teh inventory. Because this is, ultimately, a 'non-consumbale' purchase from the inventory not a 'consumable' purchase, create your own mechanism to restore inventory selections to other devices owned by that user. Be sure to tell App Review that you are allowing the user to exchange a CREDIT for an item in inventory and that you have established your own mechanism for restoring the product to other devices owned by that user. You can use the user's key-value file in iCloud for that restore function.
I am developing an app that will have a catalog of hundreds of audio items that are working with a unique Bluetooth device
(Those are not music files, and not something you can you can offer on itunes)
I want the users to be able to purchase those audio items and then they can play them
But there will be hundreds of those and I will keep add them to the catalog from my back end admin
What whould you suggest in order to build the IAP for this?
Is credits the only way ?
I thought maybe I can list all those audio items for the prices of $1, $2 and $3
Then create 3 consumable IAP IDs for the above 3 prices.
And when user is buying any item from the catalog it will bill as per those 3 IAP IDs .
And since they are “consumable” , more items from the same price can be bought
Will this way work ?
That will work fine. As I wrote above, you will need to create a method of restoring the purchase to other devices owned by the user and you should indicate to App Review that you have such a 'restore' function implemented. Although 'consumable' IAPs do not 'need' to be restored, your item is really a 'non-consumable' item that is obtained through this 'consumable transfer currency'. Therefore a restore function is appropriate.
(By the way, you could also sell the consumable in discounted packages of 5 if you wanted.)