Failed to build cordova on windows

I am building an windows app via cordova on windows10. The command I am using is cordova build windows -- --win. But I got below errors:

EXEC : warning : Start page is missing on the disk. The build must go on but note that this will cause WACK failures. [
C:\dev\ap-ui\packages\app\mobile\platforms\windows\CordovaApp.Windows10.jsproj]
MakeAppx : error : Manifest validation error: Line 36, Column 52, Reason: The file name "www\index.html" declared for e
lement "*[local-name()='Applications']/*[local-name()='Application']/*[local-name()='Extensions']/*[local-name()='Exten
sion']" doesn't exist in the package. [C:\dev\ap-ui\packages\app\mobile\platforms\windows\CordovaApp.Windows10.jsproj]
MakeAppx : error : Package creation failed. [C:\dev\ap-ui\packages\app\mobile\platforms\windows\CordovaApp.Windows10.js
proj]
MakeAppx : error : 0x80080204 - The specified package format is not valid: The package manifest is not valid. [C:\dev\a
p-ui\packages\app\mobile\platforms\windows\CordovaApp.Windows10.jsproj]

I have installed vistual studio 2017 and set the environment variable VSINSTALLDIR=C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\MSBuild\15.0\Bin

I use this command to add windows platform: cordova platform add windows

The cordova versionis "çordova": "8.0.0"