from what I can see, Squared is a card reader that you plug into your iPhone:
squareup.com/
it is for point of sale processing of the credit card, not used for on line purchases. Maybe they also offer a payment gateway service that eCart could leverage, but i don't see any evidence of that.
If there is a gateway API that is offered by square, it is not one that is supported by eCart, so you would need to hand code the logic of passing the transaction to them using the API Documentation that they provide as a guideline.
