When a product is added to the cart, a coupon code field is available. But after pressing continue to checkout, the coupon code field is no longer available. Anyway to make it appear through other steps in the checkout process?
provide coupon field at checkout cart page
donot provide coupon field at onepage (checkout/onepage).
If you want to add this last step of onepage then follow the link Magento code or extension to add coupon code in last step of onestep checkout