The debug option was already actually set to ‘False’
Here is the response from admin-ajax.php:
<!DOCTYPE HTML PUBLIC “-//IETF//DTD HTML 2.0//EN”>
<title>500 Internal Server Error</title>
<h1>Internal Server Error</h1>
The server encountered an internal error or
misconfiguration and was unable to complete
Please contact the server administrator,
and inform them of the time the error occurred,
and anything you might have done that may have
caused the error.
More information about this error may be available
in the server error log.