It may be due to any of the following reasons. Please confirm.
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If the sent authentication code is outdated
When the authentication code is sent more than once, only the last one will be valid.
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If there was an error when entering the authentication code
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If 30 minutes or more has passed since the authentication code was sent
The authentication code becomes invalid after 30 minutes or more has passed after it was sent. In such case, please have the authentication code sent again and then log in.
Use the “recovery code” if this does not help.
<Related questions>
Q. How do I have the authentication code sent again for two-factor authentication sent via email or SMS?
Q. What is a recovery code?