Trouble adding first host in AWS

My rancher server is running on an AWS instance. I want to add my first host. I’m doing all of this from the Rancher UI. I’m using Rancher 1.6.9. I’m clearly missing something, but the error message is not much help:

Error setting machine configuration from flags provided: RequestError: send request failed

From experience creating instances in AWS, I need to provide a key pair name, but I don’t see where do do that. I only entered the “required” fields on the page.

The rancher-machine security group was created, but then the process failed with the above error.

Please, advise.