Um, that's not part of this event. The email that you received was because you purchased AP for the first time, and the coupon you got is sorta like a bonus for your next AP purchase (You get 20% more as a thank-you). It's not related to this event at all.
The bonus cash is included in the purchase itself. They raised the % at the billing page for the various methods to purchase AP, specifically for this event.
[BEFORE this event]
If you purchase 1000 AP for 10 dollars with 20% bonus (at the 'Save Up To' on the billing page), you'll get 200 bonus AP. So the total AP you would receive is 1200 (1000 + 200).
[FOR this event]
They raised the amount of bonus AP you would receive by 50%. So instead of receiving 200 bonus AP, you would receive 500 bonus AP (because 1000 x 50% = 500). Your new total AP would be 1500 (1000 + 500).
Basically, they raised the bonus AP you would receive with each respective mode of payment (Paypal, Credit Card, etc). Check your billing page, it should have the updated AP bonus you'll receive prior to your purchase (look under 'Save Up To').