Continuously Rejected my Flutter Project.

Hello . I create mobile app in flutter with Laravel Backend and uploaded it. but after reviewing my item Envato team rejected my item 3rd times with message.

I will need you to significantly improve the UI of the application. It looks too barebones right now. I’m not asking for utter sophistication, just acceptable levels of refinement. If this were a class or a snippet, I wouldn’t mind if it had a bad looking demo but since this is a complete system I have to take every facet of it into account.
My Flutter apk. app-release.apk - Google Drive

please suggest me what UI changes can be helpfull for getting my item approved.Thanks