I contacted Apple Developer Relations and received a reply that Apple had actually sent the email to the relevant developers.

I have discovered that the first 52 characters of the ID of the pricePoint matches the first 52 characters of the ID of the price in manualPrices or automaticPrices. Would it be possible to use this rule?

Sorry. My previous post was wrong. I was able to get the customer prices from the "included" entry in the JSON obtained at the following URL. https://api.appstoreconnect.apple.com/v1/inAppPurchasePriceSchedules/{inapp_id}/manualPrices?include=inAppPurchasePricePoint,territory&fields[inAppPurchasePricePoints]=customerPrice