When you clicked the link and it opened up your calendar it should have displayed the date's options on the right side to accept the change. You might try clicking on the exact date to see if it gives the option.
I have actually never received an email, but have received a 10% off opportunity twice on my calendar page about specific days. Both times I accepted the offer, but still did not get booked. This last time the 10% off stopped showing the day before the date arrived.
When your listing shows on the results page there is no text or any type of icon to indicate that that listing is "on sale." After you click the listing, select the date that includes the sale, there is just one line of small text under the pink "book now" button to indicate that there is any lower cost.
Adter you accept the offer there will be a tiny medium grey icon displayed on the sale date on your calendar to indicate that that day is having a special price.