// register meta box
function meta_fields_add_meta_box(){
    add_meta_box(
        'meta_fields_meta_box', 
        __( 'Course Booking URL', 'textdomain' ), 
        'meta_fields_build_meta_box_callback', 
        'page', 
        'side',
        'default',
        // hide the meta box in Gutenberg
        array('__back_compat_meta_box' => true)
    );
}
add_action( 'add_meta_boxes', 'meta_fields_add_meta_box' );

// build meta box content
function meta_fields_build_meta_box_callback( $post ){
    wp_nonce_field( 'meta_fields_save_meta_box_data', 'meta_fields_nonce' );

    $paymenturl = get_post_meta( $post->ID, '_meta_fields_payment_url', true );
    $courseid   = get_post_meta( $post->ID, '_meta_fields_course_id', true );


   ?>
   	

	    

	        

	            Payment URL:
	        
	        

	            
	        
	    
	    

	        

	            Course ID:
	        
	        

	            
	        
	        
 
	    
	

   
A meta box gets created on a post type page in the side and shows 2 fields and values from those 2 fields would be saved in post meta once the page is saved