When installing an on-premise API Monitoring Radar Agent (previously known as Runscope Radar Agent), you may encounter an "invalid username/password" error message. 

This error is due to recent changes made to the authentication process.  The Radar Agent now requires a Runscope API token in order to properly authenticate.  You must initially run the agent program with this API token via the --token​ argument, then save the agent's configuration to a file.

To achieve this, do the following:

1. Log into Runscope.
2. Visit https://www.runscope.com/applications and create a new application by clicking the blue icon in the upper-right.
3. On the next page, provide any name for the app (perhaps something like "Runscope Agent Token" so it reflects its purpose). You can provide any website URL and callback URL -- they can even be completely imaginary, so long as they "look like" URLs to satisfy the parser on that page.
   Note: Normally this application creation process is used to set up an application for use with a an OAuth flow with a third-party app so that app can access Runscope, but it is also used to generate a Runscope API token for general Runscope API usage, which is what we're doing here.
4. Hit the Create Application button.
5. On the next page, scroll down a bit and you'll see the Personal Access Token. This is a UUID that is your Runscope API token which you'll use with the agent.

Now that you have your token, launch your agent like this:

/path/to/runscope-radar --token=whatever-your-token-is

If you are on multiple Runscope "Teams", you will be prompted to choose which "Team" to associate the agent with. If you are on only one Team, no such prompt will occur. You'll also have an option to save the Agent configuration to a file -- do this. On future runs of the Runscope agent, you'll pass it a parameter that indicates its configuration file:

/path/to/runscope-radar -f /path/to/radar.conf

Note that the agent configuration file contains various parameters, including the API token (which you provided) as well as a unique agent ID that was generated and the Team ID that the agent is associated with. You can read more about the agent and its options here:
https://www.runscope.com/docs/api-testing/agent/

That's it! you may execute your test as desired.