The Max True Peak level of the audio is too high.
When an analogue sound wave is converted into digital, samples are taken along the analogue wave. At any peak the audio level will rise (incline) and then fall (decline). At this point the highest point of the curve (The True Peak) will be higher than the two samples on the incline and decline of that curve.
This means that although the maximum possible sample level of a digital signal is 0.0dBTP, it is possible to have a True Peak above this level. In this case the file will fail QC.
Also note that the gradient of the incline and decline will affect how much the True Peak level is above the Maximum sample level.
In cases where the True Peak exceeds 0.0dBTP the audio will be clipped.
The audio level needs to be lowered. This can be done is various ways within your edit or audio suite. One option is to to identify the the loudest part of the Ad (the peak) and reduce only this segment below the peak level threshold, or alternatively the entire audio can be reduce and therefore again brining the True Peak level below the threshold.