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@pmanuel checkout Comet Chat plugin

@pmanuel make sure ; added at end of the line
define( 'WP_MEMORY_LIMIT', '256M' );

@pmanuel
you can try to paste following code in wp-config.php file just before the line that says ‘That’s all, stop editing! Happy blogging.’

define( 'WP_MEMORY_LIMIT', '256M' )
you can read more about it here.
https://www.wpbeginner.com/wp-tutorials/fix-wordpress-memory-exhausted-error-increase-php-memory/

@pmanuel inside your WordPress install, log in via FTP or SFTP
and open wp-config.php
and find line
define( 'WP_DEBUG', false );
and replace it with following
define( 'WP_DEBUG', true );

@pmanuel you can turn on debug mode using the following guide

Debugging in WordPress

any error log will help to isolate the issue.