Hi,
Have you tried to schedule your AZ-900 exam? I believe they switched from vouchers to applying the discount automatically based on your email address. Please start the process using below link (make sure email used matches same one used for Virtual Training Days):
Go through all the steps until you get to point where it is asking for payment information. Check if it shows the 50% discount. If not add a comment below and I'll give you instructions for creating support case.
Please click Accept Answer if the above was helpful.
Thanks.
-TP