IP address. The classic example is scholarly/academic journals. Access by subscribing university libraries and corporations is still generally dependent on IP address. It has been this way for as long as I can remember. Early 90s at least.
An expected retort might be "But consumer IP addresses are subject to change." True, but sometimes a "static" IP is non-negotiable. For example, in the past if one subscribed to ICANN's zone file access program, which is public information open to access by anyone, not only university libraries or corporations, a static IP address had to be provided. Of course one could use a consumer IP address because those can change infrequently, sometimes on a timescale of years. If it ever changed then one had to execute a new agreement. Perhaps the requirement for a static IP has been dropped but I honestly doubt it.
Rate-limiting/access control by IP address is common and straightforward.
However so-called "tech" companies have shown they cannot be trusted when collecting information from users. For example, Twitter and Facebook each claimed they were requesting phone numbers from users for "security" reasons but it turned out they were using them for commercial purposes.
Wouldn't they have to validate a paying customer to tie it to an IP aswell? If there is a point where a user is identifiable, it can't be rolled back with a "trust us" in my opinion if the focus is privacy.
Sometimes service providers on the internet try to accomodate "anonymous" payment via wire transfer or other non-credit card payment methods. VPNs are one example. Whether this is significantly "anonymous" is debatable. An obvious question is whether the service provider retains payment information after payment is made and if so, why. To provide service, arguably the provider only needs to know "this IP address is paid up through [date]". It does not need to know "this IP address is associated with [user]". It does not need to collect or retain any information about [user].
