Hi All , me again...
I'm trying to add a link to the left navigation menu using an HTTP request as below but it's not working.

I have even tried these slight variations:
Adding the IsExternal and making it true then providing an absolute URL or setting is as false and providing a relative URL or jsut excluding it completely.
{
"__metadata": { type: "SP.NavigationNode" },
"IsExternal": true,
"Title": "BBC",
"Url": "https://bbc.co.uk"
}
The seems to be, if I provide the correct full URL, it just keeps running for minutes till it times out or I cancel it. However when I provide an incorrect URL, e.g. missing a / somewhere in it, it works and adds the link instantly, but it's a non-working link to nothing. I'm stumped!
Your help is much appreciated