What goes in the id/BTCUSD field for Mt. Gox "submit an order" API call? I am trying to place a new order using Mt. Gox's submit an order API call. However I keep on getting the error object 

{ result: 'error', error: 'Bad API call' }


I'm fairly certain I'm doing everything right, except I suppose the order Id which is referred to as BTCUSD in the documentation. 

https://data.mtgox.com/api/1/BTCUSD/private/order/add


It gives no other explanation on what this field is, and I have found other projects calling it ID, so I'm using the node-uuid v1() method to generate a unique ID for the field.

So this is the URL I create:

/api/1/36c1f990-a4a4-11e2-84fd-a100a9f27dd2/private/order/add


and the object I send with it

{ type: 'ask', amount_int: '100000.000', price_int: '20000000' }


What am I doing wrong?
This field is used to spcify the currency pair type of the return data, so leaving in BTCUSD works fine or changing it to a different accepted currency pair, such as BTCEUR, also works and just changes the currency denomination of the returned data.