If your country (in business profile) is not set to United States, you cannot create a coupon code in USD. Unfortunately, GoHighLevel does not support changing the currency for coupons currently, as it is tied to the Business Profile settings and there is no option to override it when creating a coupon.
So if your business address is not in the United States, there is no way for you to create a USD coupon code.
A workaround could be to change your country to United States, but then all emails such as invoices would show your business address as United States.