404 error using excel vba

I am new to using an API. I was having a problem logging in but solved that from reading comments on this support page. I now get a ‘404’ error so I think I must be getting the link construction wrong. My code constructs the URL as:
https://api.routexl.com/tour,locations=[{“address”:“Warehouse”,“lat”:“53.7665244”,“lng”:"-0.3304322"},{“address”:“Benenden C of E Primary School, Benenden Road, Beneden, Cranbrook, TN17 4EH”,“lat”:“51.0655159”,“lng”:“0.5790961”},{“address”:“Goudhurst and Kilndown Primary School, Beaman Close, Cranbrook Road, Goudhurst, TN17 1DZ”,“lat”:“51.1141263”,“lng”:“0.4680623”},{“address”:“Warehouse”,“lat”:“53.7665244”,“lng”:"-0.3304322"}]

I then send it using Excel VBA with this code:
Dim oHttp As Object
Set oHttp = CreateObject(“MSXML2.ServerXMLHTTP”)
Call oHttp.Open(“POST”, fn, False)
If (authUser <> vbNullString) Then
oHttp.setRequestHeader “Content-Type”, “application/json”
oHttp.setRequestHeader “Accept”, “application/json”
oHttp.setRequestHeader “Authorization”, “Basic " + _
EncodeBase64(authUser & “:” & authPass)
End If
Call oHttp.send(”")
httpGET = oHttp.responseText
Set oHttp = Nothing

and get the return message as:

404 Page Not Foundbody{margin:0;padding:30px;font:12px/1.5 Helvetica,Arial,Verdana,sans-serif;}h1{margin:0;font-size:48px;font-weight:normal;line-height:48px;}strong{display:inline-block;width:65px;}

404 Page Not Found

The page you are looking for could not be found. Check the address bar to ensure your URL is spelled correctly. If all else fails, you can visit our home page at the link below.

Visit the Home Page

I would be grateful for any help.

Thank you

We’re no VBA experts, but the constructed link seems wrong to us. It adds locations to the endpoint, resulting in an nonexisting path. That would explain the 404. We’d expect the locations to be added only in the send() command.

See: How to perform an HTTP POST request in ASP? - Stack Overflow

Note: the request should not be JSON encoded, only the value of the locations parameter should be JSON.