When doing a receipt validation, Fovea’s response will contain an ineligible_for_introprice array, which is parsed by the cordova plugin to fill product.ineligibleForIntroPrice for all ineligible products. See the plugin documentation about ineligibleForIntroPrice here: https://github.com/j3k0/cordova-plugin-purchase/blob/master/doc/api.md
For this to work, you need to make sure your app validates the application receipt. It’s only after application receipt validation that the eligibility information will be made available.
When making use of introductory offers, it’s also recommended to call store.update() when entering your In-App Purchase screen. This ensures that you’re retrieving the most up-to-date information.