When the keyboard hides, a black screen to appear in the gradient background

We’re developing an iOS application using Ionic React and are utilizing the default keyboard. The app features a full-screen gradient shape moving animation. When the keyboard retracts, a black screen becomes visible at the bottom part of the screen. Its height is less than that of the keyboard, suggesting that the webview height adjusts when the keyboard shows/hides. Please advise on how to remedy this issue.

Here is motion: IMG_2747 (2).mp4 - Google Drive

Thank you.