Best answer by Ryan S
Glad you're interested in more Sonos! To be eligible for the promotion, you must first have received an email from Sonos containing a unique coupon code for you to use. The coupon is mainly intended for use on sonos.com but can also be used to claim back 20% from a purchase made in retail, only if the purchase was made after you received the promotional email. Not everyone received one of these emails.
Please see below the Eligibility criteria as laid out in the Terms & Conditions found here: https://sonos-welcome.com/us/en/pages/cashback/terms
We'll leave this topic open in case someone has a spare code they want to offer to others, but we don't have any available at this time to share ourselves.