502 Bad Gateway When Install Flarum

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I have this problem when i install flarum,i need your help,thx!

Littlegolden

This is the screen shoot，Security group has released ports 888 (phpMyadmin), 3306 (MySQL).
Using：

CentOS 7.7.1908(Py2.7.5)　
Nginx 1.17.9
PHP 7.4
MySQL 5.7.29
phpMyadmin 4.9

Nginx log：

bind() to 0.0.0.0:3306 failed (98: Address already in use)

Now, we restart the server, and will try change a port of MySQL to see if it will be solved.

luceos

Littlegolden bad gateway means php-fpm is down.

Using a different port on MySQL isn't really a solution, better would be to try to identify what is reserving that port because only MySQL should use it.