Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
1
When if you paid Microsoft directly for the Microsoft 365 subscription, that licence should have become associated to your Microsoft Account as a digital licence online and it is from there that you can install Office without the need for a product key:
https://account.microsoft.com/services/
Do you find your subscription on that link?
2
If you are not actually installing Office, if you are experiencing problems using the Office apps, please provide a screenshot of any error you may be seeing.
Also, what is the exact version of your operating system.