There does not seem to be an easy way to add an initial price (or customer price) to a blank subscription whether that is during creation or updating after. I have been successful in initiating a price change after I set a random price first by hand, but even after following Apples guidelines, I seem to be using the wrong endpoint or json data to give the subscription a new price from an empty one.
I am trying to use this endpoint to add a price point with all of the possible territories.
PATCH https://api.appstoreconnect.apple.com/v1/subscriptions/{id}
A price change will work if the price has been previously set and POST https://api.appstoreconnect.apple.com/v1/subscriptionPrices is called but, setting the initial price with the api is the issue.
Any Information would be helpful. Thanks!