I wanted to chime in with the perspective of someone who works for Facebook. For most businesses, even ones that host pages for other businesses, Aggregated Event Measurement without anything extra is the correct solution.
Advertisers who do not own their own domains will not be able to verify the domain for the purpose of event configuration in Ads Manager. Advertisers may consider purchasing their own domain to continue running their campaigns uninterrupted, or moving toward link clicks/landing page views for campaign optimization and reporting. We are currently investigating other solutions for this use case but do not have any additional information to share at this time.
For a very small number of businesses already on the Public Suffix List (PSL) subdomains will be able to get data as if they were a root domain. This is because being on the PSL basically makes the root domain name act as if it was a TLD (such as “co.uk“ or ”gov.au“). In almost every case it does not make sense for sites to request to be added to the PSL as this dramatically changes how the Public Suffix listed domain name will function.
The PSL process is intended only for platform providers that provide subdomains for large numbers of small businesses which really ought to be treated as though they were in fact separate domains.
The Public Suffix List is not useful, nor intended to be used as a means to gain additional subdomain events reporting. Adding a domain name to the PSL means that there will be total cookie separation between subdomains and that cookies will become disabled on the root domain. If you a domain gets added to the PSL you'll not have much control for that site itself. For example, if you have a /login page on that domain. This may not work as it does today if you proceeded with a PSL addition, as cookies may get disabled on the root domain.
It’s also important to note that browsers will enforce the behavior described based on their own update cadence of the PSL. Some browsers don't update their lists more regularly than bi-annually. This means that if you're on the list and a browser updates their copy of the list, and you later decide to not be on the list, there may not be an easy way to back out the effects; it's not as simple as submitting another request to get taken off of the list.
More information can be found at Facebook’s help center article here.
