If your app has been published and you cannot purchase an in-app purchase using an iOS device, make sure you have done the following:
- Do you have a Apple Paid Apps contract in effect?
- Have you checked Cleared for Sale for your product?
- Are there any contracts waiting for approval in your App Store Connect?
- Do the In-App Purchases have all fields filled (including screenshots)?
- Did you set a price that is not "USD 0 (Free)"?
- Did you wait 24 hours?
- Are your bank details active on iTunes Connect?
- Have you tried deleting the app from your device and reinstalling?
- Is your device jailbroken? If so, you need to revert the jailbreak.