In the Discounts sub-tab, you can build out different Promos or Discount codes to apply to specific Services/Packages, Payment options, or just as a Checkout Discount. Here you would provide a Name, Discount type (Flat or Percent), Minimum Order Value and Maximum, Enable/Disable Checkout Discount, and choose Payment Type.
If you enable a Discount as a "Checkout Discount" then your customers will be required to put in the case-sensitive name of the Discount at checkout for it to apply. If you have Geopricing enabled in the Integrations tab and Add-on sub-tab, you have the option to select the Region you would like the Discount to apply.
If you want to apply a Discount directly to a service or package ensure that for "Checkout Discount" you put disabled. When this is set to disabled, then customers do not input the discount code at checkout, it is automaticlaly applied based on the specific services/package you add it to.
To add Discounts to a Service, click on a service and go to Discounts. From there, all your discounts that you set to disabled for "Checkout Discount" will appear. If for any reason you do not see a discount you created, go back to the Discounts sub-tab and ensure that this is option is set to disabled.
To add Discounts to a Package, click on the package you would like to add a discount to. On this page, you can choose to add the Discount to a specific application or the entire package. If you want to add it to a specific application, click on the services section and then on the "Discounts" button that is on that line item. If instead you want to apply a discount to the entire package, go into the discounts section under that specific Package and add the discount there. You can add multiple discounts and also remove discounts by deselecting them at any time.
This is also briefly covered in the Discounts tutorial at the 43 second mark: