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Have you tried to clear the browser cache? You could also try to empty the session folder. In most cases, that should solve the issue, at least if it worked before. Also make sure that you don’t have the Panel open in multiple tabs.
If this doesn’t work, please provide some more information:
- Is this on first trying Kirby or have you been able to log in to the Panel previously and now it has stopped working
- Which Kirby version are you using and in which environment (locally, remote server)
- Your PHP version
The output from phpinfo() could also be useful.
What do you get as HTTP response in your browser’s network tab? See also Can not log in to panel - Invalid CSRF token - #12 by lukasbestle