While working on WordPress, the most common issue is a PHP Fatal error regarding the allowed memory size of xxxxxxx bytes exhausted visible by any debugging tool.
This error is reported by PHP when a PHP file is processing too much load than the set limit. There must be lots of plugins active or the theme you are using is bulky & PHP memory isnt enough to handle these things. There are simple ways of increasing the memory allocation of your website.

Solution 1: Edit PHP.ini

If you’re still allowed to edit your PHP.ini file, update your memory_limit in PHP.ini by modifying the below line:
memory_limit = 64M ; Maximum amount of memory a script may consume (64MB)
If the line is showing 64M in default, try 128M.

Solution 2: Edit .htaccess file

If you don’t have access to PHP.ini, you can try adding following line code to an .htaccess file. Add the script below to your .htaccess file.

php_value memory_limit 64M

Solution 3: Edit wp-config.php file

Add the script below to your wp-config.php file

Increasing memory allocated to PHP
define('WP_MEMORY_LIMIT', '64M');