"Uncaught" error trying to do simple Harmony commands

I’ve got a Vizio soundbar that times out after 10 minutes of silence. That’s pretty easy to achieve by pausing a movie or the DVR to get a sandwich or deal with the dogs or the bathroom or whatever.

So I’m trying to create a simple-as-anything entity-button card in Lovelace that sends one lousy Harmony command to power-toggle the soundbar. Right now, the code is in a script file because I’ve tried everything short of voodoo to make this work.

I get the button with a great big remote control icon (to be changed), but when I press it, I get notified that the log has been written and I don’t get my power toggle. The log entry just says

Tue Oct 30 2018 04:25:13 GMT-0500 (Central Daylight Time)
http://hassbian.local:8123/frontend_es5/app-b01b9b58.js:1219:80438 Uncaught

I have no idea what “Uncaught” means or how to debug it. My card and script are ultra-simple:

Card:

- type: entity-button
    title: Toggle Sound
    entity: script.vizio_toggle

Script

vizio_toggle:
  sequence:
  - service: remote.send_command
    data:
      entity_id: remote.harmony_hub
      device: 41961817
      command: 'PowerToggle'

I can confirm that these are the right commands by sending them through the manual JSON-firing tool.

Anyone know what I have wrong?