Fill in your payment information and click REVIEW MY ORDER.
You will find the coupon box on the left hand side of the page as pictured. Click the line that reads ENTER A CODE. When you do, a box will drop down where you can enter the code
Manufacturer coupons are not generally accepted at Target.com, as these are issued by the manufacturer not Target.com. If a coupon is accepted on Target.com, it will include an alpha-numeric promo code that you enter during checkout as shown in step 8 (for example, TGTXXXXX).
If the manufacturer coupon you want to use is not recognized by Target.com, then your only option is to use it at your local brick and mortar Target store.