In your ads manager, go to your pixel page

Here you will see your pixel activity

The number of pixel fires is the amount of time a behaviour such as a page visit happened. Five page visits could've come from one person looking at multiple pages on your website. 

Underneath the chart, you can see the events broken up to behaviours

Here it's saying that in the last 7 days, there were 541211 Pages looked at. But not how many unique visitors who have looked at them. 

If you look at the column "Status", you will see when the last event was fired. If that is in more than 1 day and you are seeing results in another analytics software, that is a good indication that your pixel isn't working. 

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