Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
If you have entered your new subscription code and no errors were indicated like the code has been previously used, try logging out of your Microsoft account online, wait a small while, then log back into your account and check the expiry date on your Microsoft 365 subscription to see if it has been updated, if not, how long has it been since you entered the new subscription code?