First define the pixel under Tracking Pixels in your dashboard: choose the provider (Meta, Google Ads, Google Analytics, TikTok, LinkedIn, X, Snapchat, Pinterest, Reddit, Quora, AdRoll, Bing) and enter the ID from that platform.
Then, when creating or editing a link, pick your pixel under Targeting Pixels. You can attach more than one pixel to the same link.
If the ID is wrong, events simply will not be tracked and you will not get an error. Verify it with the platform's own testing tool after you add it.