You need to complete 1 x challenge to get an exam voucher, though it is worth it considering that exam vouchers are usually US$165. This voucher is valid for a lot of exams, only close thing to this I have seen is free Azure Fundamentals voucher for 5 hour webinar.
Eligible exams: https://docs.microsoft.com/en-us/learn/certifications/micros...
"Participate in the Microsoft Ignite Cloud Skills Challenge to earn a free Microsoft Certification exam and a chance to win prizes! Choose up to six different challenges to complete on Microsoft Learn. After you’ve completed your first challenge, you’ll earn a free Microsoft Certification exam. For each challenge you complete, you’ll earn five entries into a sweepstakes. One grand prize winner will receive a chance to meet with a Microsoft leader and invite up to four friends."
"How does the challenge work?
The Microsoft Ignite Cloud Skills Challenge is comprised of six, subject specific challenges. You can participate in as many as you’d like—the more you complete, the more sweepstakes entries you earn.
Each challenge is based on a specific collection of Microsoft Learn modules. Finish the collection before the challenge closes to earn sweepstakes entries and credit for your completion."
"Free Microsoft Certification exam
After you've completed your first challenge, you'll earn a free Microsoft Certification exam. The exam will be associated with this account for use starting on October 14, 2020. If your Learn account is different that the account you use for Microsoft Certifications, that's okay—you'll have the opportunity to link your account when you redeem this prize."