The issue you are running into is covered in the community FAQ, so you will want to take a look at that. It gives you the exact sequence of steps that you need to do to authorize the device and explains why you need a device which is both a switch and a sensor.
But the short answer for others who might have run into this is that at the present time Alexa routines (not smartthings routines) cannot be triggered by a switch at all. Only by a sensor.
What the FAQ is going to do is show you how to create a virtual device which is both a switch and a sensor. When you turn on the switch, the sensor will look like it opened. When you close the switch the sensor will look like it closed. The sensor part of the Device can then be used to trigger an Alexa routine. 
It will also give you the exact sequence of steps that you need to follow in order to get that virtual device visible to Alexa routines.
(It sounds like you found the right virtual device, you just didn’t follow the full sequence for authorization the first time.)
Here’s the FAQ (the topic title is a clickable link)