probably because I bought it online from another legit site
Should not make any difference. You'll need to sign on using the same account used for activation. Another option
https://support.microsoft.com/en-us/topic/how-to-replace-microsoft-software-or-hardware-and-order-service-packs-924dea3c-1304-6145-2753-1201ca352893
--please don't forget to upvote
and Accept as answer
if the reply is helpful--
All Office 2021 direct download link:
Office 2021 Home Student :
http://officecdn.microsoft.com/pr/492350f6-3a01-4f97-b9c0-c7c6ddf67d60/media/en-US/HomeStudent2021Retail.img
Office 2021 Home Busienss:
http://officecdn.microsoft.com/pr/492350f6-3a01-4f97-b9c0-c7c6ddf67d60/media/en-US/HomeBusiness2021Retail.img
Office 2021 Professional:
http://officecdn.microsoft.com/pr/492350f6-3a01-4f97-b9c0-c7c6ddf67d60/media/en-US/Professional2021Retail.img
Office 2021 Professional Plus :
http://officecdn.microsoft.com/pr/492350f6-3a01-4f97-b9c0-c7c6ddf67d60/media/en-US/ProPlus2021Retail.img
Office 2021 Mac :
https://officecdnmac.microsoft.com/pr/C1297A47-86C4-4C1F-97FA-950631F94777/MacAutoupdate/Microsoft_Office_16.53.21091200_BusinessPro_Installer.pkg
I found these download link from the microsoft partner store keyingo.com, it seems all the links are directly from Microsoft.com, so it is legit , you can copy the download link to browser , then it will start to download