Hi Muhammad,
For Microsoft Virtual Training Days the 50% offer is not a traditional voucher code. It is tied to the Microsoft account that attended the event and is applied automatically when you schedule the exam from the personalized link in the email.
Open the email, select the Schedule or Claim your discount link, sign in with the same Microsoft account you used for the training, make sure your Certification profile uses that same email, then choose your exam and select At a test center if you want an in-person appointment. The discounted price will show on the Pearson VUE checkout page without any code, and the test center does not need a voucher from you.
If the discount does not appear, first confirm the training email address exactly matches the email on your Microsoft Certification profile, then try the link again while signed in to that same account. If it still does not show, contact Microsoft Certification Support with the Virtual Training Days confirmation email so they can attach the discount to your profile.
Let me know if this helps please!