If you have a redeem code, you can register the redeem code as follows.
1. Important: Before entering the redemption code, you must set up your account in OfficeMail app because the redemption(redeem) code has been issued for the email address you requested. It will be used as a primary account in OfficeMail service that will be able to manage your additional accounts and devices. This primary account will be used as a billing account later.
2. You probably received a redeem code by email. Then go to the site (officemail.app) with a browser on your desktop computer and log in to the OfficeMail service.
3. You will get an email from OfficeMail service to confirm if the account you tried to sign in would be a primary account. Go to your email app and click the button "Sign in".
4. Now, OfficeMail's site will be open again with a new window. You can check that you are logged in with the email account. Click the account icon on the top right, select "Settings".
5. In the left panel of Settings, click "Billing".
6. Now, you can see the Billing page and find the "Redeem" button on the top right. Click the "Redeem" button.
7. The Redeem code popup will be opened. You can input the redeem code you received in the email.
8. If clicking "Redeem" button after inputting the redeem code, all redeem code registration will be done. You can see the message that your subscription has been activated through the redeem code normally. It's all done.