Since July 7, IRCC has requested that all applicants to provide an upfront medical exam.Sadly I don't see any upload link, and the medical center doesn't allow me to schedule an appointment without an IME letter.
The medical center should provide you with an upfront medical exam as a federal worker. I did mine like that when I applied. Maybe they have not been informed of the new changes.
*Note: Try opening your profile using you mobile browser, just to be sure. Sometime their website works best in mobiles. I didn my payments using the mobile version because the desktop one didn't show me the payment page to complete it.