ItemList error in SDTT: "All values provided for url must point to the same page" - schema.org

Question

I'm trying to add the ItemList Schema.org markup on an article page that lists top 10 software with (external) links pointing to them.
When I tested the following JSON-LD markup on SDTT, I got the error message saying
All values provided for url must point to the same page
I don't really understand why the individual list items should use the same URL?!
{
"#context": "http://schema.org",
"#type": "ItemList",
"name": "Title of the page",
"description": "Description goes here",
"itemListElement": [
{
"#type": "ListItem",
"position": 1,
"item": {
"name": "Product 1",
"image": "https://www.product-1.com/image",
"URL": "https://www.product-1.com"
}
},
{
"#type": "ListItem",
"position": 2,
"item": {
"name": "Product 2",
"image": "https://www.product-2.com/image",
"URL": "https://www.product-2.com"
}
}
]
}
</script>
I used a slightly different markup without the "item": { as put in https://developers.google.com/search/docs/guides/mark-up-listings, but this time I'm getting an error message that says
All values provided for url must have the same domain
Can you please help me solve this problem?
{
"#context":"https://schema.org",
"#type":"ItemList",
"name": "Title of the page",
"description": "Description goes here",
"itemListElement":[
{
"#type":"ListItem",
"position":1,
"name": "Product 1",
"image": "https://www.product-1.com/image",
"URL": "https://www.product-1.com"
},
{
"#type":"ListItem",
"position":2,
"name": "Product 2",
"image": "https://www.product-2.com/image",
"URL": "https://www.product-2.com"
}
]
}

Answer 1

These errors are about Google’s Carousels feature. This feature requires certain url values:
If used on a summary page, all URLs in the list must point to different pages on the same domain.
If used on an all-in-one-page list, all URLs must point to the page hosting the list structured data.
Your case (linking to external sites) is simply not eligible for getting the Carousels feature in Google Search. You can (and should) keep your JSON-LD like this and ignore these errors in the SDTT.