When the Facebook pixel is installed on a website, and the pixel uses first-party cookies, the pixel automatically saves a unique identifier to an
_fbp cookie for the website domain if one does not already exist.
When a user clicks on an ad on Facebook, the link sometimes includes a
fbclid query parameter. When the user lands on the target website, if the website has a Facebook pixel that uses first-party cookies, the pixel automatically saves the
fbclid query parameter to an
_fbc cookie for that website domain. See About Cookie Settings For Your Facebook Pixel for information on first-party cookie settings.
We recommend that you always send
_fbp browser cookie values in the
fbp event parameters, respectively, when available.
_fbc browser cookie is not available, either because there is no Facebook pixel running on the website or because first-party cookies are turned off, it is still possible to send the
fbc event parameter if an
fbclid query parameter is in the URL of the current page request.
fbc event parameter value must be of the form: version.subdomainIndex.creationTime.fbclid
_fbccookie, use the value 1.
fbclidquery parameter in the page URL.
Here’s an example of what the
fbc value could look like (note that the
fbclid portion is invalid):