Meta Business Help Centre
Troubleshoot audience count and pixel traffic differences
Audience counts reported by website Custom Audiences only measure unique visitors matched to accounts across Meta technologies within the time frame that you choose (up to 180 days). They also exclude people who opt out of ads based on website and/or app usage.
The Meta pixel traffic reported in your pixel dashboard measures the number of times that your pixel is fired (even if it's by one person multiple times or traffic that didn't come from a person across Meta technologies) within the time frame that you choose (the last seven days by default).
Because of these differences in measurement, counts may vary between the two.