Hi iryna,
Thank you for contacting the Microsoft Community.
Regarding your first query, during the exam registration it is recommended to register with Pearson VUE to take advantage of the Azure Virtual Training Day discount. Additional details on how to schedule for an exam can be found on this link.
To register and apply your discount, you will need to sign-in using your personal Microsoft Account in the Certification Profile, once done, there will be a field under “Exam Discounts” to enter the registered email used in the event. Once done, kindly check this instructional video and follow the step by step instructions on how you can link your email address and check the eligibility of the discount on your email.
Meanwhile, the $15 offer is delivered by PSI for candidates who are affected with the pandemic. To take advantage of the MAVTD discount, please select Pearson VUE.
If you have issues claiming your discount, please follow the steps recommended on this sticky post.
Should you encounter issues after the recommendations above, please send us a step by step recording using Problem Steps Recorder (PSR) starting from the troubleshooting steps and until you received the page where it shows "No discount available" for both events, as well as your Event ID, and Congratulatory Emails so we can check your eligibility for the discount.
Kindly upload your PSR through the private message I initiated along with the requested information.

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. Thank you.
Regards,