Creating new subscribers

I am trying to programmatically add a subscriber. I am using PHP and the HTTP POST curl method which works for me when creatig a free account for users - however when adding a new subscriber I'm getting a 404 with the message 'There is no subscriber with a customer id of <my>'.

I've checked the url, the xml that's being posted and have debugged to my hearts content - but can't see the answer.

The url I'm usng is:

https://<token>@spreedly.com/api/v4/<testaccountname>/subscribers.xml

The xml I'm posting looks like this:

<subscriber><customer-id><currentuser /></customer-id><screen-name><currentname>-<currentsurname /></currentname></screen-name></subscriber>

Can you shed any light??

John
</testaccountname></token></my>