Poloniex API Problem

I'm having problems with the Poloniex API, when I run the code

polo = poloniex.Poloniex('key', 'secret')
polo.sell('BTC_MoedaX', 0.003, 3)
polo.buy('BTC_MoedaX', 0.003, 3)

Returns the error:

{'error': 'Amount must be at least 0.000001.'}

But the amount indicated in the third parameter is greater than 0.000001 and still returns this error.

Edit: API documentation: link Code that I'm using: link (the same as available in the documentation, but instead of urllib I use the request.