Sirmadsen Glad you found the cause. đź‘Ť
That actually makes sense because Flarum’s Extension Manager uses Composer underneath, and Composer can require significantly more PHP memory while resolving dependencies or installing/updating extensions. Flarum’s documentation confirms that the Extension Manager is essentially a web interface for Composer.
So the 500 error was most likely PHP hitting the configured memory_limit, rather than the Extension Manager itself being broken.
For anyone experiencing the same issue on cPanel, check MultiPHP INI Editor / PHP Options → memory_limit and increase it if it is set very low. Composer’s own documentation specifically recommends increasing PHP’s memory limit when you encounter Allowed memory size exhausted errors.
It would also be worth checking the server error log to confirm there is a message similar to:
PHP Fatal error: Allowed memory size ... exhausted
If increasing the limit fixed everything and the forum is now stable, I’d still keep an eye on the logs during the next extension install/update rather than assuming every future 500 error is memory-related.
