Because changing your date doesn't move your original due date — and your Pay Now page counts from that original date. So even after your reschedule goes through, the page will still show your second Split Pay payment as past due. That's expected, not a sign that anything went wrong.
The confirmation we send you when your date changes is what counts. As long as you received that confirmation, your new date is in place and you're all set — the "overdue" label is just reflecting that your original due date has already passed, not that your new date didn't take.
When your new date comes around and the payment goes through, the past-due status clears on its own.
If you didn't get a confirmation, or something still looks off, contact our Support team and we'll check it for you.