Hi,
After 5 business days you should be able to see the 100% discount if you schedule the AZ-900 exam. Have you tried scheduling it yet (it's a little early but might be there already)? When you get to discounts screen it should look similar to below:
If the above doesn't help please ask your question in the Microsoft Certification forum using link below. There are support moderators over there that will respond to your question in 1 business day and can assist with getting your discount to show up:
https://trainingsupport.microsoft.com/en-us/newthread?threadtype=Questions&forum=mcp
Please click Accept Answer if above was helpful.
Thanks.
-TP