Hello Frederic,
Based on the information you have provided, you are signing in using your professional email reason why you are unable to register for the exam.
To proceed in scheduling the exam, please make sure to sign in using your personal/Microsoft account. Once done, there will be an option to enter and verify your professional email address.
You may follow this Instructional Video in claiming the discount.
Typically, the discount will reflect to your profile 5 business days after the event has concluded before you can use your exam discount.
In any case that the discount is not reflecting to your profile, please send us a step by step screenshot from the time you signed in up to the discount page. Please use the Problem Steps Recorder (PSR) for the screenshots.
You may upload the screenshots to the private message I initiated along with the requested information.
To access your private message, please refer on the image below:

I look forward to your response. Please note that if no response is received after two business days, the case will be closed and locked. After the case is locked, we will no longer be able to respond, even through Private Messages.
Thank you,