Shopping Carts, Marketplaces and Order managers normally treat coupons like line items in the order. They'll show up during packing which slows things down. While it's not possible to prevent them from being imported it is possible to hide them from the packer. You can set individual items to "intangible" by clicking on their product name in the product list (or anywhere else you find the product name) this will open the product details page. Click the second tab at the top of the window, scan & pack options, and you'll see a switch for "Intangible Item". Enable this and the product will be hidden from the packer.
Sometimes you'll have a zillion discount codes but they will all have something in common, a few letters in their SKU or Product name. For these we can set GroovePacker to automatically identify these and hide them from the packer.
This option can be found in Settings > System Settings > Scan and Pack Options. It's called "Auto Recognize Intangible Items". When you enable it you'll be able to add the "string" that identifies your coupons. For example if your coupons were named, COUP-001, COUP-002, COUP-003, you could put COUP- in the field.
Most of the time coupon items will not have a barcode either, which will cause them to appear in the "New" list. The SKU of the item can be added as a placeholder barcode for these items. Rather than assigning these manually you can enable the next switch marked: Auto-Generate Barcode for Intangible Items.