Sorry, I don't know terraform well.
Is this resource related to the new platform zones?
Because if it is, scopes are mandatory, and they can be 1 or more.
On L:52 I see MaxItems:1 .
Also scopes ids are missing 🤔
This is an example response from staging:

// ....
"scopes": [
    {
        "id": 439653,
        "rules": "",
        "targetType": "azure"
    },
    {
        "id": 439654,
        "rules": "",
        "targetType": "kubernetes"
    },
    {
        "id": 439655,
        "rules": "",
        "targetType": "host"
    }
]

thanks for checking! yes, this resource is for creating new platform zones, but since it's only for secure currently it is named like other secure resources.
I changed scopes to be required field and also I added id as a field for scope... nice catch! 👍
MaxItems:1 is for "scopes" field - we can have only one of those. MinItems: 1 is set for "scope", because we need at least one of them.

I removed scopes to simplify the schema