What should I use for profile in backend API when I don't have an email or phone number?

​@jnema if neither email nor phone number can be used a an identifier, you can leverage external id.  More info here

Essentially you can pass it like below for the call:

{ "data": { "type": "profile", "attributes": { "external_id": "1414951756", "first_name": "Sarah", "last_name": "Mason" }, "properties": { "birthday": "1989-12-13T00:00:00Z" } } }

Hope this makes sense.  Let me know if you have any questions.

I wouldn’t use an external id here. This will just create records separate from the original profile.

​@jnema, it sounds like you’re looking to log events for profiles that are identified by klaviyo on the client but you don’t have their email on your side? Can you share more details on your app and the kinds of events you’re looking to trigger here? Assuming you have some kind of client access to leverage the results of a klaviyo.identify() call, I’m wondering whether you might be able to hook up these events client side. 

While technically possible, I wouldn’t recommend relying on undocumented Klaviyo identifiers directly as they’re liable to change and break your app.