Anonymous53 look for the error message in the log file or with debug mode https://docs.flarum.org/troubleshoot
Do you have SSH access? If so, run composer remove <package> or composer install if you already updated composer.json to fix the state of dependencies.
Please give us as much information as you can about your hosting. If you have SSH, are you able to run php flarum info. Apart from that, which PHP version, MySQL version, shared/dedicated hosting?
Have you successfully installed other extensions before?
If you have a backup, consider restoring and trying again, possibly with debug mode on so you get a better idea of what the problem is if it happens again.
