It is likely just a temporary issue. Since you said you already entered a product key then the key is tied to your MS account. Go to your MS account in the browser. You can get there by clicking your profile in the Edge browser assuming you are using the same MS account for Windows. Alternatively go to https://account.microsoft.com and sign in.
Once signed in, if you have an MS 365 subscription, then you can install directly from the main page. If you purchased a retail copy of Office then scroll down to the Products you've purchased
section and it should be there. The install link should be available.
If you don't see it there then click the Apps button in the top left corner and click on More Apps. On this page is the Install Apps
link that will get you to the installer.
Alternatively go to Order history
and find the purchase.