SEOPress manual FAQ Schema + Metabox.io – Use related custom FAQ post type

functions.php

/**
 * FAQ Schema.org for MetaBox Relationship if manual FAQ Schema is active
 * 
 * @See https://www.seopress.org/support/hooks/filter-manual-faq-schema/
 */ 
add_filter('seopress_pro_get_json_data_faq','sp_pro_schema_faq_json', 10, 2);

function sp_pro_schema_faq_json($json, $context)
{
    $relationship_id = 'faq-page'; // Replace with your Relationship ID
    $question_id = FALSE; // Replace with your Answer Field ID or FALSE if post title should be used
    $answer_id = 'faq_answer'; // Replace with your Answer Field ID
    
    $show_all_if_nonrelated = FALSE; // Show all FAQ if there is no FAQ related to this post
    
    $faqs = new WP_Query( [
        'relationship' => [
            'id'   => $relationship_id,
            'from' => get_the_ID(),
        ],
        'nopaging'  => true,
        'order'     => 'ASC',
        'orderby'   => 'menu_order',
    ] );
    
    unset($json['mainEntity']);
	$json['mainEntity'] = [];
	
	if(!$faqs->have_posts()) {
	    if(!$show_all_if_nonrelated) {
    	    // If we don't have FAQ related to this post, do not return FAQ schema
    	    return $json;
	    } else {
    	    // If we don't have FAQ related to this post, get all FAQ
    	    $faqs = new WP_Query( [
                'post_type' => 'faq',
                'nopaging'  => true,
                'order'     => 'ASC',
                'orderby'   => 'menu_order',
            ] );
	    }
	}
	
    while ( $faqs->have_posts() ) {
        
        $faqs->the_post();
        
        $question = ($question_id) ? rwmb_meta($answer_id) : get_the_title();  // Replace with your FAQ "Question" field value
        $answer = rwmb_meta($answer_id); // Replace with your FAQ "Answer" field value
        
        $faq_question = esc_attr(stripslashes_deep(wp_filter_nohtml_kses(wp_strip_all_tags(strip_shortcodes( $question )))));
        $faq_answer = esc_attr(stripslashes_deep(wp_filter_nohtml_kses(wp_strip_all_tags(strip_shortcodes( $answer ))))); 
        
        // Needed if FAQ answer is a wysiwyg editor
		$faq_answer = str_replace("\n", '<br />', normalize_whitespace($faq_answer));
		
		$faq[] = [
			'@type' => 'Question',
			'name' => $faq_question,
			'answerCount' => 1,
			'acceptedAnswer' =>
			[
				'@type' => 'Answer',
				'text' => $faq_answer,
			],
		];
    }
    wp_reset_postdata();
    
    $json['mainEntity'] = $faq;
    
	return $json;
}