Set Environment Variable [Developer or Production Mode] (M2)

First, will be a good idea to check the current MODE:

The main idea is to have this (environment) variable MAGE_MODE set to one of this values: Default Developer Production   To change the MODE in Magento for the moment there are 3 ways: From CLI  (you'll be 100% sure it changed)

Using the .htaccess file:

Through your WEB…