How can I manage dynamic content with In-App Purcahse ?

As long as you are not using the Apple Servers to provide the content, a simple approach is to handle this accounting yourself within the app. You can do that by creating a consumable item 'Tokens'. You can sell '1 Token' or '5 Tokens' at a discount. The user can buy multiple packages of 1 or 5 tokens. The app keeps a count of how many Tokens the user has purchased. To download content the user picks a set of numbers that get recorded in the app. Each number picked causes a reduction in the number of Tokens by 1. Once the Tokens have been all used up the user cannot select any further numbers until they buy more tokens.

we are using a similiar approach for our dynamic content, where we have set up consumables in every price range so that if there is a new content added in the backend, the app chooses the consumable that matches the price (or the one nearest to i). this works so far, but the question is, how can the restore of those products be done - for users that are not registered within the app - since its a requirement? is it possible to send the transaction receipt to the backend and then use it to check if the product was already bougt, and restore it?

You can use the user's iCloud key-value file to record their purchases and restore them to other devices logged into the same iCloud account. A device that needs to 'restore' does not have access to the receipt.

is the icloud file the only way? if a user logged in with the same apple id wouldn't he get the same receipt for a purchase? if that is the case it should be possible to store a receipt on the backend and then deliver the same content again if the user submits the according receipt?