Internal Promotion CTR is a Metric in Google Analytics under the Ecommerce section
Internal Promotion CTR Definition: The rate at which users clicked through to view the internal promotion (ga:internalPromotionClicks / ga:internalPromotionViews) – (Enhanced Ecommerce).
How its calculated: ga:internalPromotionClicks / ga:internalPromotionViews
Data Analytics & Insights Google Analytics Metrics Internal Promotion CTR