In many cases, you will encounter an admin-ajax.php 500 error, which is a common ajax call error in WordPress for many reasons, such as software version, software environment, and so on.
If you want to find the source of the problem, you must check PHP’s error log. Of course, you can look for it in the website Host cPanel(Not WordPress wp-admin), and if you can’t find the log, you can view it through Error Log Monitor plugin.
Please go to Plugins>Add New, enter “error log” to search, find the Error Log Monitor, click Install, click Activate after it is downloaded.
Go to WordPress Dashboard, there would be a tip to guide you edit the config.php file, you should login website host FTP to edit the config.php, it is in WordPress root folder. If you don’t have FTP. Please login your website host cPanel, most of host suppliers would have a webFTP tools.
After the configuration is complete, the log will appear in your WordPress Dashboard.