When running different functionalities in the plugin or in the installer, a request could fail and you could get a status code in the (ajax) error message.HTTP response status codes indicate whether a specific HTTP request has been successfully completed. Responses are grouped in five classes.

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Solution 1500 errors are generic in nature and can be difficult to isolate. These errors can be related to file permissions, ownership rights, firewall/proxy configurationconstraints or a server that is not configured correctly. Below is a list of starting points to isolate the issue:

ERROR LOGS:
In many cases error logs are critical with 500 errors. The best place to start is by checking to see if there are any clues in the error logs.

1. WordPress Error Log: Occasionally there are incompatibilities with the new web server and the site itself (PHP version changes for instance).To track down the problem capture an WordPress error log while you refresh the page causing the error.See this article for how to capture the WordPress error log.
2. cPanel Error Log: If your host is running cPanel, click on the “Errors” icon to review the latest errors experienced on the server.
3. Web Server Logs: These include the PHP error log and your web server error log such as Apache or Nginx. To find these files consult yourhosts documentation. To find the latest errors match the correct time stamp in the error log with the time for which you were attempting touse the Duplicator. Sometimes error logmessages can be vague and a quick Google search for the actual error message many times will leadto a quick resolution, especially if you include your hosting providers name.

WHERE DO YOU SEE THE 500 ERROR?:
A 500 error can be experienced either during the package build process, during the install process or post-install. Below are some helpful tips depending on where you experiencea 500 error.

1. During Package Build:
   • Disable Plugins: In some cases certain plugins (especially security and caching) will prevent certain actions from happening.If you have a security or caching plugin installed itsrecommended to temporarily disable it to make sure its not conflicting with anything.
   • Create Filter: Sometimes creating a root directory filter will allow the package to skip any files or directories that are problematicto how PHP is able to process and read them. This test step can help you isolate which directory (if any) might be triggering a 500 error.
   • open_basedir: The php.ini setting can cause all kinds of issues if not properly configured. See question:What is PHP Open Base Dir or “open_basedir restriction in effect”?
2. During Install:
   • Disable Plugins: If the 500 error is present on the installer side then its recommend to create your package withall cache and security plugins disabled andadd all cache paths to the directory filters list.
     Note: The directories filter has a quick add link for cached WordPress data.
   • If you receive a 500 error during the installation process see the FAQ item below:
     How to resolve 403/500/timeout issues on step 3?
3. Post-Install:
   If you experience a 500 error or blank screen when loading a site after installation, please review one of the logs mentioned in the “ERROR LOGS” section above.

Also See:
How to resolve 403/500/timeout issues on step 3?
How to Fix the 500 Internal Server Error on Your WordPress Website
Recommended hosting providers for Duplicator?