I have hosted my website in Firebase and I'm using [myappname].web.app free domain. I have android app associated with it and willing to publish it on google play-store. Is it ok to use app.web.[myappname] as the package name for it. Are there any legal issues since I'm not owning the web.app domain.
Yes it's okay. The package name of an Android app can be anything you want, as long as it doesn't exist yet.