Add one Sonos One to the cart. In the cart, change the quantity to 2.

This is not where you can talk to folks in the ordering department of Sonos, so you may need to call in. 

That being said, usually discounts are on a single line item, and not multiples of speakers. If you could find a pair of Sonos Ones as a single item to order, that discount code might work. It likely will not work on two items….but then again, I’ve not seen anything about the restrictions on that particular discount code.