Hello Waleed,
Thank you for contacting us here at Microsoft Community.
Based on your given description, you are entitled for a voucher less discount which should be applied by linking the email address used in the event to your certification profile.
If you are unable to redeem the discounts, you may follow the troubleshooting 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.
Once done, you can follow the instructions on the instructional video provided on this thread and check what email address needs to be linked on your profile through this link.
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 attach the confirmation/congratulatory email you received after completing the training.
The information will be forwarded to our Support Team for further investigation and resolution.
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.
Regards,