This article refers to the Hermes extension for Magento 1, not Magento 2.
When using the Hermes extension for Magento 1, this error occurs:
Hermes API is currently not available. Please try again later.
The Hermes extension for Magento 1 is not maintained anymore. Due to the age (last update was in 2015), the extension cannot communicate with the current Hermes API.
Because Hermes currently only commissioned the development, maintenance and support for the Magento 2 extension, no updates or bugfixes can be provided for the Magento 1 variant.