If you want the ambassador to receive a product before completing the mission, you must make sure you set this up when creating the mission. This is easily done by turning on the option "Deliver a product to user before mission submission" and follow the steps.
If you wish to add an additional award like cash or a gift card after the mission is completed then you must untick the box "This is the only reward for this mission". You will then be given the option to add an additional reward in the next step (Reward).
Please find below a video which shows how to create a seeding mission with a free product delivered before the submission and option to give an extra reward, in this case cash, once the mission is completed: