我已经完成了一个项目，我想建立一个apk。我试图建立它，但在写句子建立它，第三个代码给了我一个错误。这里的代码或句子我写的是建立它。

ionic cordova platform remove android
ionic cordova plarform add android@6.4.0
ionic cordova build android

我已经建立了一个项目3天前以下的代码我wrode以上。这里的错误。（这次我连接与firebase）

Platform android already added.
[ERROR] An error occurred while running subprocess cordova.

        cordova platform add android@6.4.0 --save exited with exit code 1.

        Re-running this command with the --verbose flag may provide more information.

E:\ionic\notasFirebase>ionic cordova build android
> ionic-app-scripts build --target cordova --platform android
[19:08:57]  ionic-app-scripts 3.2.0
[19:08:57]  build dev started ...
[19:08:57]  clean started ...
[19:08:57]  clean finished in 13 ms
[19:08:57]  copy started ...
[19:08:57]  deeplinks started ...
[19:08:57]  deeplinks finished in 61 ms
[19:08:57]  transpile started ...
[19:09:03]  transpile finished in 6.09 s
[19:09:03]  preprocess started ...
[19:09:03]  preprocess finished in 1 ms
[19:09:03]  webpack started ...
[19:09:03]  copy finished in 6.41 s
[19:09:11]  webpack finished in 8.34 s
[19:09:11]  sass started ...
[19:09:13]  sass finished in 1.66 s
[19:09:13]  postprocess started ...
[19:09:13]  postprocess finished in 29 ms
[19:09:13]  lint started ...
[19:09:13]  build dev finished in 16.44 s
[19:09:19]  lint finished in 6.02 s
> cordova build android
Unable to load PlatformApi from platform. Error: Cannot find module 'E:\ionic\notasFirebase\platforms\android\cordova\Api.js'
Unhandled error. (The platform "android" does not appear to be a valid cordova platform. It is missing API.js. android not supported.)