Please see similar question posted here - https://trainingsupport.microsoft.com/en-us/mcp/forum/all/discount-code-for-the-exam-az-900/a62987ac-7dec-4846-a95a-c8c79506c858
You can also post your own question separately on same site.
If the response helped, do "Accept Answer" and upvote it - Vaibhav