The peak level of the Audio is too loud.
The audio level must not go above a defined maximum level, if it does at any point in the Ad the file will fail QC. Peak level measurement differs from Average Loudness measurement, which is now used in most countries. It is also different from True Peak.
Please check the Peach Connect File Specifications required for the region and Ad type you are trying to upload.
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 bringing the peak level below the threshold.
Peak Level is an older method used to measure audio levels but is still used in some countries.
e.g. Spain -10dB
There is no lower limit so technically the ad can be mute and would pass QC.