Go to https://app.zappost.com/and log into your account.
Go to your settings by clicking on cog picture found in the horizontal menu at the top of the page.
This will take you to the Settings page. On the lefthand side of the page, there is a menu. Click on Api Consumers found near the bottom of the menu.
This will take you to the Api Consumers page. Click on Add New Consumer button, found near the top of the page.
A pop-up box will appear. Give it a name and click the enabled slider on.
Note down the Api Key and Password and click on create consumer.
The api key and api password should be added to the username and password fields respectively when installing the app;
The environment selected should be "production" as shown above.