Sql agent job fails with access denied error

We are trying to execute a SQL agent job which executes a step to shut down a service on DEV ENV using CMDexec, but it fails with error below:

Executed as user: ABC\mssql. System error 5 has occurred. Access is denied. Process Exit Code 2. The step failed.

I have added above user in admin group and even in Logins given the sufficient privileges. yet it fails with same reason.

Moreover we tried changing the owner of the job to SA, surprisingly the job still fails with same error: listing the ABC/mssql as the user.

Kindly help