Hello Henry,
Thank you for contacting us here at Microsoft Community.
Please note that you can redeem the exam discount after 5 business days (Excluding Saturday and Sunday) from the completion of your training.
Recently, there’s a known issue in claiming the discount for Ignite Cloud Skills Challenge March 2021 and Microsoft Virtual Training Day events which was already resolved and fixed as per our Engineering Team. You may refer to this sticky post.
If you’re still unable to claim the discount, you may follow the steps below:
Make sure you have the latest browser (Edge/Chrome/IE or Mozilla Firefox)
Try using your browser in InPrivate/Incognito
Clear browser cache and cookies
Allow all cookies/third party cookies on your browser settings
Sign back in to your Microsoft Certification profile and try to update/schedule your exam.
For Ignite Cloud Skills Challenge 2021, you may follow the steps from this link: Microsoft Ignite Cloud Skills Challenge 2021: Free Certification Exam
If the above steps do not resolve your issue, please send us a step by step screenshot using Problem Steps Recorder (PSR) starting from the steps above and until you received the error.
You may upload your PSR through the private message I initiated along with the requested information.
To access your private message, please refer on the image below or click on this link.

Also, in the private message, please do not forget to attach the confirmation/congratulatory email you received after completing the event.
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.
Regards,