1. You are trying to type in a password or phone number field. Note that Apple does not allow third-party keyboards to type in these fields. This way, Apple ensures that your privacy is protected and your data remains secure.
  2. You removed the keyboard app. If you remove the app, you automatically also remove the keyboard along with its settings.

Using the same App Store account that you used to purchase Keeble, you can redownload the app for free. For instructions, please see this Apple support document.