It is normal for the numbers not to match 1:1. Here are the most common reasons.

Accepted event ≠ attributed to the campaign

Events Manager shows "the event has arrived".
Ads Manager shows events that have been attributed to the ads (according to the attribution window and reporting rules). Therefore, some events may only be in Events Manager.

Attribution window and reporting settings

If a purchase occurred after the attribution window (for example, "click 7 days"), it may not be included in the campaign, even though the event exists.

Delays and data processing

Ads Manager may display data with a delay; Events Manager often shows reception/flow faster.

Privacy/consent/browser restrictions

Some users block cookies/trackers or do not give consent — this worsens matching and attribution.