Why isn't a discount applying to the shipping cost when an order posts to NetSuite?

If you have a discount applying to the entire order including the shipping cost in the marketplace/cart and it doesn't apply to the shipping cost when the order posts to NetSuite, then this indicates that the SuitePromotions feature is most likely enabled in NetSuite. When this feature is enabled, promotions applied at the transaction level will only be applied to the transaction subtotal. This means, for example, tax and shipping costs will not be discounted.

There are two different solutions to remedy the issue.

1. You can create two separate promotions in the marketplace/cart - one for the order amount and one for the shipping amount. If you have a promotion specifically for the shipping amount, SuitePromotions will be able to apply it to the shipping cost in NetSuite. These promo codes must have matching promo codes in NetSuite (https://support.farapp.com/hc/en-us/articles/360038362293-How-to-set-up-matching-Promo-Codes-from-the-marketplace-cart-to-NetSuite). The SuitePromotions checkbox in FarApp should also be checked under NetSuite > Settings > General (https://app.farapp.com/settings#/netsuite_settings).
2. You could disable SuitePromotions in NetSuite which will allow NetSuite to apply discounts to tax and shipping amounts. SuitePromotions can be enabled/disabled under Setup > Company > Enable Features > Transactions > Sales > SuitePromotions.