Updating a users settings via the Rest API in v10 doesn't seem to work

Hi, 

I'm trying to update the value of "ReceiveEmails" to false and am following the documentation here:

https://community.telligent.com/community/10/w/api-documentation/61739/update-user-rest-endpoint

However I get 404 - File or directory not found.

This is my code as a Powershell script:

$Url = 'https://mysite.com/api.ashx/v2/users/testuser.json';

$Payload = '{"Id": "3012", "ReceiveEmails": false}';

$Response = Invoke-WebRequest -Method POST -URI $Url -Body $Payload -ContentType "application/json";

I can create a user with similar code to the above fine but for some reason I can't get update to work.

I've read a number of forum posts here but not found a solution.

Thanks

Adam