Set environment variable Staging and given error production.ERROR: No application encryption key has been specified in Laravel 5.5

I am using Laravel 5.5 and I have set the environment variable "Staging" and every time has given error "production.ERROR: No application encryption key has been specified"

New key generated and config cache clear all possible scenarios I already tried.

APP_ENV=staging
APP_KEY=base64:t5nAnqh5ZBCT4SXxcENyDs+fx399Tq1YecP1Z9At850=
APP_DEBUG=true

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