"Direct Music Streaming Isn't Supported" Error

[SMac3265]

I'm almost there! I got past the "500 Internal Service" error and I have an automation set up to play a sound effect when a specific trigger is enabled. Now - my Echo Dot is complaining that "Direct Music Streaming Isn't Supported", something that is set by Amazon, and not my AMP or HA. I'm attempting to play a sound effect, about 7 sec long. My "type" is set to music. If I change the type to "sound", I do not get an error, but the sound never plays, either. In my config, I've tried just the filename.mp3, then doing local/filename.mp3, and finally, the entire path, http://192.168.50.14:8123/local/filename.mp3. No errors, but no sound, either. I feel like I'm THIS CLOSE to making it work.

Oh, and if I go that URL in the browser, the sound plays fine, so that path is a good one.

Sean