From time to time, Nutanix announce that some certifications has free vouchers available.

Some times they appear behind the certifications you are allow to schedule.

Take a look here at the community and also at your certifications tab at the Nutanix University top page.

So far, I did not notice any vouchers offer yet.

Watch the blog https://next.nutanix.com/education-blog-153 for announcements of voucher programs - note that the number of free vouchers has been greatly reduced in recent years.   Right now only way is a free voucher when you buy an ILT course.  You can also ask your rep (sales rep for customers or relationship rep for partners).

Also, watch for beta exams or the launch of new exams.   Although if you want NCPMCI, the latest version went live in December. So the next beta / new launch is over a year away.