Create SharePoint List (CreateSPList) setting the List icon

I'm using HTTP to Sharepoint with CreateSPList to build list on a new site, based on a list from an existing site. (I'm actually using Power Automate at the moment...)

It works well, except for the fact that my List Icon parameter does not seem to work. I always get the "broken image link" icon displayed:

I'm setting the CreateSPList "icon" parameter with the URL of the site icon, which I know exists:

...
"addNavLink":true,
"description":"RAG List",
"icon":"https://[OrgNameHere].sharepoint.com/sites/[SiteNameHere]/_api/siteiconmanager/getsitelogo",
"listName":"RAG"
...

as shown in the JSON Schema description here:  https://developer.microsoft.com/json-schemas/sp/site-design-script-actions.schema.json   (Line #114 or thereabouts)

Have I got the syntax wrong for the value of the "icon" key?  Anyone got any ideas? I'll be exceedingly grateful - it's been baffling me for hours... well, days!