Take extra data when someone click on "I am attending"

code.php

<?php

add_filter( 'eab-rsvps-button-no', 'get_req_form', 10 );
function get_req_form( $content ){
	global $post;
	
	if( is_user_logged_in() )
		$form = '<div class="sp_req_wrap"><textarea name="sp_req" placeholder="Special Request"></textarea></div>';
	else
		$form = '';
	$content = $form . $content;

	if( is_super_admin() ) {
		$req = '<h3>Special Requests</h3>';
		ob_start();
		sp_req_callback( $post );
		$req .= ob_get_clean();
	}
	else{
		$req = '';
	}
	
	return $req . $content;
}

add_action( 'wp_footer', 'events_req_style' );
function events_req_style() {
	?>
	<style>
	.sp_req_wrap{
		margin: 20px 0;
	}
	.sp_req_wrap, .sp_req_wrap textarea{
		width: 95%;
		height: 100px;
	}
	.wpmudevevents-buttons{
		float: none !important;
	}
	</style>
	<?php
}

add_action( 'incsub_event_booking_yes', 'incsub_event_booking_yes_cb', 20, 2 );
function incsub_event_booking_yes_cb( $event_id, $user_id ) {
	$temp = get_post_meta( $event_id, 'sp_req', true );
	
	if( ! is_array( $temp ) ) $temp = array();
	
	$temp[] = array(
		      'user_id' => $user_id,
		      'sp_req' => $_POST['sp_req']
		      );
	
	update_post_meta( $event_id, 'sp_req', $temp );
	
}

add_action( 'add_meta_boxes', 'ev_add_meta_box' );
function ev_add_meta_box() {
	add_meta_box(
			'ev_sp_req',
			'Special Requests',
			'sp_req_callback',
			'incsub_event',
			'advanced',
			'high'
		);
}

function sp_req_callback( $post ) {
	$reqs = get_post_meta( $post->ID, 'sp_req', true );
	
	$html = '<table cellpadding="5" cellspacing="5" width="100%">';
	$html .= '<tr>';
	$html .= '<th width="20%" style="text-align: left">Username';
	$html .= '</th>';
	$html .= '<th style="text-align: left">Request';
	$html .= '</th>';
	$html .= '</tr>';
	foreach( $reqs as $req ){
		$user_info = get_userdata( $req['user_id'] );
		$html .= '<tr>';
			$html .= '<td>';
				$html .= $user_info->display_name . ' (' . $user_info->user_login . ')';
			$html .= '</td>';
			$html .= '<td>';
				$html .= $req['sp_req'];
			$html .= '</td>';
		$html .= '</tr>';
	}
	$html .= '</table>';
	
	echo $html;
}