Why do direct metrics differ between "Medium-specific details" and "Campaign performance"?
The medium-specific breakdown (e.g., Banners, Paid Search, etc.) reflects what is directly attributed to each individual ad click. The Campaign Performance view uses the retailer's complete sales dataset.
Because these two views come from different data sources, small differences in the numbers are expected and normal. Both figures are correct - they simply reflect different ways of capturing and attributing the same underlying sales activity.