Thanks @Anonymous . Seems the answer is here:
https://trainingsupport.microsoft.com/en-us/mcp/forum/all/101620-offer-redemption-email-not-received-after/08221af9-261a-4e88-baa9-ddcca5a9fb42
10/16/20 1:15pm PST: Although the free exam availability period began on October 14th, 2020, some customers may not have yet received the congratulatory email providing instructions for offer redemption because they have not provided an email address on their Learn profile to be used specifically for notifications.
If you have successfully completed an Ignite Cloud Skills Challenge but have not received your mail, please contact Microsoft Ignite CSC Help at IngiteCSCHelp@microsoft.com and provide the following information.
Your Learn User Name (you may retrieve this from your Learn profile, or copy and paste it from this link)
The email address at which you wish to receive your redemption instructions
A screenshot of your completed Ignite Cloud Skills Challenge Leaderboard (example below).
You will be added as an eligible customer and will receive your free exam redemption link within the following week.