functions.php

<?php
// ^ there should only be one of these at the very top of your functions.php file.
// Omit the <?php above if adding this code to the bottom of your functions.php file (and one exists already at the top)

// Add one filter before Field Editor to make sure required shows as disabled in list table
add_filter( 'submit_job_form_fields', 'smyles_set_job_description_not_required', 99 );
// Add another one to actually set the value after Field Editor updates fields
add_filter( 'submit_job_form_fields', 'smyles_set_job_description_not_required', 101 );

function smyles_set_job_description_not_required( $fields ){
	
	if( is_array( $fields ) && ! empty( $fields['job'] ) ){
		
		if( ! empty( $fields['job']['job_description'] ) ){
			$fields['job']['job_description']['required'] = false;
		}
		
	}

	return $fields;
}

// This filter handles preventing fatal error from empty value in post_content
add_filter( 'submit_job_form_save_job_data', 'submit_listing_allow_empty_job_description', 99999, 5 );

/**
 * Allow empty Listing Description (job_description) field in WP Job Manager
 *
 * If you're using the Field Editor plugin, and want to configure the Description (job_description meta key) field
 * to only show for specific packages, you will need this code to prevent a white screen of death, as the core
 * WP Job Manager plugin requires this value to not be NULL.  This function will filter the core WP Job Manager
 * job data, and set the post_content (used for job_description meta key) to an empty string, instead of NULL.
 *
 *
 * @param $job_data
 * @param $post_title
 * @param $post_content
 * @param $status
 * @param $values
 *
 * @return mixed
 */
function submit_listing_allow_empty_job_description( $job_data, $post_title, $post_content, $status, $values ){

	/**
	 * If we disabled the job_description meta key field, the post_content value will be NULL,
	 * so we set it to an empty string to prevent any fatal PHP errors.
	 */
	if( $job_data['post_content'] === NULL ) {
		$job_data['post_content'] = '';
	}

	return $job_data;
}