Plugin says that there is no route

Robert reported today that he got an error saying that the REST API has no route. Here is how he had fixed it:

What the “route” is:

SNIP uses WordPress’ internal REST-API. It allows to exchange data back and forth between WordPress an SNIP. This is also used for activating and deactivating the plugin. If a route is not available there it means that there is something wrong with your WordPress configuration.

The solution:

Robert solved the issue by configuring the .htaccess file. A solution was posted on StackOverflow. Look it up there.