Promolayer and GA4 measure different metrics using different methods, so the numbers are not expected to match exactly.
Getting Started
First, please check whether the scope being compared is aligned between the two:
Target pages (pages where the Display is shown)
Date range and time zone
If a discrepancy remains even after confirming the scope matches, the cause depends on the direction of the difference.
Cases where Promolayer's view count is lower than GA4's pageview count
Different counting definitions — GA4 counts a pageview every time a page loads. Promolayer, on the other hand, only counts a "view" when all display conditions (device, targeting, re-display frequency, whether the visitor has already converted, etc.) are met and the display is actually rendered on screen. For details, please see "How are views counted?".
Cases where Promolayer's view count is higher than GA4's pageview count
Differences in bot/crawler exclusion scope — GA4 automatically excludes traffic based on an extensive, industry-standard list of bots and crawlers. Promolayer also excludes some major crawlers (such as bots from large search engines), but its exclusion scope is more limited than GA4's. As a result, crawler traffic that GA4 excludes but Promolayer does not gets included in the view count, which is one reason Promolayer's numbers can exceed GA4's pageview count.