If you are getting an Authentication Error when Logging in to the Untapped.gg Companion, your credentials might be full.

To solve this issue you can follow these steps:
1) Go to your Credential manager
2) Back up your Existing Windows Credentials
3) Try deleting several Windows Credentials (including the Untapped.gg one if exists)
4) Reboot
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If after doing this your problem persists, please email us at support@untapped.gg providing the Log File. You can find the Log file here