Slack OAuth Error: Invalid client_id parameter

Hi guys! I'm getting this OAuth Error: Invalid client_id parameter after I insert the user creds.
Here is my code contains the client_id -
devise.rb:
config.omniauth :slack,
Rails.application.credentials.slack[:client_id],
Rails.application.credentials.slack[:client_secret],
scope: 'identity.basic'

Let me know if there's any more infor you need from me. Thankyou for your help.