After you added an account in your authenticator application you don't need to scan QR code again. All you have to do is:
Step 1. Log in with your credentials (username and password) as usual. The second factor authentication page will open.
Step 2. Now you have 2 options:
1 Option. Open your mobile authenticator app, choose the right account (if there are more than 1) and enter the code from the mobile app to the Confluence Login page.
2 Option. If you don't have your mobile authenticator app click Enter a two-factor reserve key. Use your backup (recovery) codes and enter one-time secret password.
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