How can I use my sandbox account to test in-app purchases?

Hello - Please review this documentation with details for Sandbox testing in a TestFlight build of your app: https://developer.apple.com/documentation/storekit/testing-in-app-purchases-with-sandbox#Sign-in-to-your-Sandbox-Apple-Account-for-a-TestFlight-app

Related documentation to review:

• Overview of testing in Sandbox
• Enabling developer mode on a device
• Testing at all stages of development with Xcode and the sandbox
• Testing subscriptions and in-app purchases in TestFlight

Please let us know if you have any additional questions or need further assistance.

Thank you.

I have created a new Sandbox account in Users and Access and then I have added the new Sandbox account in my Developer settings on my iPad Air. I have tested my in-app purchases in debug mode on my iPad Air and then the Sandbox account is automatically used for the in-app purchases.

But the problem is that when I download my game from TestFlight on my iPad Air then my Apple Developer account is automatically used for in-app purchases instead of my new Sandbox account and I don´t know how to change this behaviour.

Is it possible to use the Sandbox account for in-app purchases when I install my game from TestFlight on my iPad Air?