Can't run any scripts

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I first installed Home Assistant last night and I've tried running several different scripts that I've found online but none work. I get an error like this when I try to save any of them:
Message malformed: extra keys not allowed @ data['sequence'][0]['mode']
Currently I'm trying to follow this guide, https://peyanski.com/home-assistant-google-cast-home-assistant-cast-how-to/, I create a "New Script" and I'm not sure what I'm missing. Do I need to set up something in the configuration or go through a particular menu option?

[floral fjord]

I just copied and pasted that same script into my instance and it works fine

are you using an ancient version of Home Assistant?

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Should be the latest:
Installation method
Home Assistant OS
Core
2025.8.1
Supervisor
2025.08.1
Operating System
16.1
Frontend
20250811.0

[floral fjord]

I can't figure out where you're pasting that

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Settings > About

[floral fjord]

if you're going to paste YAML directly, you need to select "Edit in YAML" from the three-dot menu

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That's what I did

[floral fjord]

your screenshot is not from that section

note that you still have the "Add action" button below

you are here:

you're trying to paste the whole script into a single action

Select "Edit in YAML" from the three-dot menu at the top right

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That's what "Edit in YAML" gives me.

[floral fjord]

again, you're just in an action

top right of the screen

keep going up and right

[safe bramble]

I already hate this interface...
Thanks