There are 3 things to check if the user is not seeing ads appearing on the output.
Firstly, in order for ads to appear on any production the user MUST be using an Graphics + Brands feature from those that are available within LIGR. If the match is set to be using a Free or Graphics feature it isn't possible to display ads on live matches. An article outlining the different types of features LIGR offer in terms of Bundles & Singles can be found here. The type of feature assigned to a match can be checked on the Matches page of the LIGR dashboard as displayed in the image below.
Secondly, if the user is happy they have an Graphics + Brands feature selected but still aren't seeing ads displayed, check the allocation of the ad set that you're trying to display. Access the available Ad Sets in your dashboard by selecting the Ads icon in the left hand navigation bar, as displayed in the image below. A detailed explanation of Ad Set Allocation within LIGR can be found here.
Finally, if the two steps above look correct, check which mode your match is set to. Auto or Manual. In Auto mode ads will display automatically based on the allocation that has been set when events are triggered. In Manual mode the automatic displaying of ads will not work, the operator will need to attach ads to particular graphics from within the Control Center. A video below demonstrates how that is done.