For developers who are having this issue with their Testflight builds i've found a workaround.
Go to the In-app page.
Select you In-app
Press the "Price Schedule" + button
Select the "Custom Price Change"
Set "Effective Date" to "Make Price Change Now"
Choose "Manually manage prices in specific countries or regions"
Select the countries where you have Testflight users.
Choose a price.
Topic:
App & System Services
SubTopic:
StoreKit
Tags: