Magento 2 API – Swagger Can’t read from file

When you use swagger as your testing tool for the API, it is possible that you get the error Can’t read from file. This can easily be solved by installing the Experius ApiExtend module:

https://github.com/experius/Magento-2-Module-Experius-ApiExtend 

The reason that this error occurs is because you have changed the storecode default to a custom store code. You can solve the problem easily in your own template by adding the following file to your custom theme, but of course  I recommend to install the Experius ApiExtend module.

app / design / frontend / Vendor/ your_theme_here / Magento_Swagger / templates / swagger-ui / index.phtml