These are two different ways of passing data. The “data to send” field is asking for a specific record in your database, which becomes required when you set the receiving page to a specific type. I’m going to assume a page called Customer Profile means that page is set to type User. So, you’d want to fill that out with “Parent Group’s Appointment’s Customer”
Once you’ve done that, everything on the page can pull from the “Current Page’s Customer” (very much like a popup acting as a data source for whatever type of thing you set… Vehicle, Appointment, etc.). /This would eliminate your need to use the URL parameter you have below, which is always an optional thing.
URL parameters give you the flexibility to pass multiple pieces of data to another page, or at least, a different type of data that isn’t the same type as the receiving page. You can also send non-database values like plain text, numbers, dates, custom state values, etc.
In sum, because your customer_profile page has a type set to it, you need to fill out the data to send. Send a customer entry (or user?). Or, you can use the URL parameter if you wish to handle all your identifying logic, but just remove the data type from the customer_profile page.
People send data to pages differently for various reasons. From what I’m gathering, I personally think it’ll be easier if you just keep your page type and send data via the “data to send” and not via the URL. Because once you’re on the customer_profile page, everything can just pull from “Current Page’s Customer [field]” as opposed to looking up a customer every time via the URL parameter - it might even slow your app down depending on how many elements you have performing that search over and over again.