Step 1: Create a URL with UTM parameters:
Example: *https://newsletterdeepdives.beehiiv.com/?utm_source=meta&utm_medium=lalaudience&utm_campaign=a31*
UTM_source = Traffic source (Meta or Twitter)
UTM_medium = your ad set
UTM_campaign = your ad
This way, you’ll be able to track down to the ad where the subscriber came from.