TechTimeRo this happens because your database table prefix is too long.
Flarum automatically creates database index names based on table names + column names, and when extensions use long column or table names, this increases the risk of creating too long index names.
There is unfortunately no easy solution to the problem. You can either manually create the index and add the migration name to the list of migrations that have been run, or modify your database table prefix. First solution requires digging into the migration files and comparing them with your database to make sure you changed everything correctly manually, while the second option requires renaming every table and index in the existing database. A third option would be to temporarily edit the migration files to hard-code a valid prefix name. Both first and third option might cause a migration rollback to fail (if you ever want to erase the extension data).
If this is a new Flarum installation, I suggest re-installing and choosing a shorter prefix. If you need to preserve the existing database we can try to provide help but it's going to require some tinkering with the database.
