Enter a Subway coupon or promo code in the promo code box that appears after you select your online order. The box is on the page that shows your order summary immediately before asking for your payment information.
Complete an online Subway order by going to Subway.com and clicking Order Online at the top of the page. Click the yellow and green Start Your Order button. Find local Subways by entering your location information, and select Order Now under your preferred store. Add items to your order. At this point, the promo code box appear on the right side of the page beneath your order summary. Enter the coupon or promo code and click Apply. Complete your order by clicking Go To Payment, entering your payment information and clicking Place Order.