Android SDK error - CommandInvokationFailure,Unity Android SDK Error - Commandinvokationfailure

I am trying to develop android apps using Unity, but there is an error.(CommandInvokationFailure)

How should I fix it?,I am using Unity to develop android apps, but there is an error on Android SDK.
It sais CommandInvokationFailure - Unable to list target platforms.
What should I do to fix it?

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