Review or Create a Discount Item

To review current Discount Item records:

1. Log in to NetSuite ERP as an administrator.
2. Go to Lists > Accounting > Items.
3. Review the list for a Discount Item that meets your needs, such as Amount Off or Percent Off.
4. If a Discount Item matching the discount type needed for your promotion does not exist, follow the next steps to create it.

You can reuse Discount Items in other promotions.

To create a new Discount Item record:

1. Log in to NetSuite ERP as an administrator.
2. Go to Lists > Accounting > Items > New.
3. Click Discount.
4. In the Item Name/Number field, enter a descriptive name. You will see this name as a discount line in transaction records generated from the discount in NetSuite. You will also select this when creating the promotion record.

For example, if you are creating a summer promotion with a 10% off discount, you can name the discount Summer Sale 10% Off.

5. Enter the discount rate to be applied. The rate can be either a percentage or a dollar amount. A percentage discount must be followed by a % sign. A dollar amount should be entered as a positive number.

For example, enter 10% for a Percent Off the regular price, 5.00 for an Amount Off. For a Price Override, set the Rate at 0.00.

6. Under RA Custom Fields, for Reduction Type, select the type of discount to apply:
   • Amount Off to apply a flat discount.
   • Percent Off to discount the item price by a percent.
   • Price Override to replace a current price with a new price.

Note: 

If you are creating a complex promotion (BOGO or Mix and Match), select the discount type to apply to the bonus item.

Example 1: If the promotion is to buy one, get one at 50% off, then select Percent Off.

Example 2: If the promotion is to buy two and receive a third at a reduced price of $10, select Price Override. The bonus item will be set to $10.00 no matter what its current price is.

6. Transaction Amount Off to apply a flat discount to the transaction total.
7. Transaction Percent Off to discount the transaction total by a percent.

7. On the Accounting subtab, under Accounts, select Non-posting if you want this discount to be non-posting.

Or, select Account and choose the account to which you want the discount to post.

Note: 

Accounting settings for discounts triggered by a promotion may be very important to your company. If you are unsure how to proceed, see Discount Items online in NetSuite and consult your accounting department before assigning these values.

8. Select the Tax Schedule to apply to this discount. Check the Apply Before Sales Tax option if applicable.
9. Click Save.

The steps above describe setting up Discount Items for use with NetSuite POS Promotions.

Reference : https://docs.oracle.com/en/cloud/saas/netsuite/ns-online-help/section_1497969716.html