(FAQ) Can products at thank-you page offers be added to the current order without inserting information again?
Why offer on thankyou page can't apply discount?
Last Update a year ago
Unfortunately this feature is really limited at the moment. BigCommerce API Promotion works based on triggering product in the cart.
Basically, the cart must have at least one product so that the API can be triggerred. With regard to the Thank you page, it shows up after one order is completed, which means your cart is now empty and the API is unable to be triggerred.