App Store Connect will not allow an in-app purchase to be added to an existing iPhone iOS app

The fundamental question is: How can I add an in-app purchase to an existing iOS app on App Store Connect?

1. On App Store Connect -> Apps -> Your App -> Monetization -> In-App Purchases there is a message Your first in-app purchase must be submitted with a new app version. Create your in-app purchase, then select it from the app’s In-App Purchases and Subscriptions section on the version page before submitting the version to App Review. (OKAY)

2. However, on the app's version page with "Prepare for Submission" status, there is no place to select the in-app purchase that was created earlier. The section "In-App Purchases and Subscriptions" is completely missing from the version page. (PROBLEM)

3. A previous attempt to submit the app resulted in this rejection: We have returned your in-app purchase products to you as the required binary was not submitted. When you are ready to submit the binary, please resubmit the in-app purchase products with the binary. (PROBLEM)

Any advice is appreciated!