Ionic v1 project build error

When I want to build my android project its show this error message any help please…

The onesignal plugin you are using does not work with Cordova Android 7.x. You might need to install a newer version of the plugin, or downgrade Cordova Android to 6.x. (The file structure changed with this update, the
AndroidManifest.xml is now in an app subfolder)

please,can you explain this issue to me in more details ??

Read this:

I really appreciate your help after I downgrade my corodva to 6.1 version I have an error in sdk location ionic can’t find sdk and when I return back to version 8 every thing work well but the same error message of onesignal plugin appear again … any help please???

Talk to the authors of the plugin you are using, look at the issues on Github.