Susa38 on "[Plugin: All-in-One Event Calendar] Custom MySQL query?"

if I insert
$post_id = $instance->get('post')->post_id;

and after I insert
get_the_post_thumbnail($post_id, 'single-post-thumbnail');

it does not show nothing

if I insert $post_id to print the post_id it does not show nothing

foreach ( $date['events']['notallday'] as $instance ) {
				$post_title   = $instance->get( 'post' )->post_title;
				$post_name    = $instance->get( 'post' )->post_name;
				$post_id = $instance->get('post')->post_id;
				$instance_id  = $instance->get( 'instance_id' );
				$content     .= '<div class="hp-event">
					<a href="ai1ec_event/'.$post_name.'/?instance_id='.$instance_id.'">'
					.$post_title.'</a><br />'.$post_id.'<br /><a class="read-more-link"  href="ai1ec_event/'.$post_name.'/?instance_id='.$instance_id.'">read more</a>
					</div>';
		}

But if I insert instance_id it print it

foreach ( $date['events']['notallday'] as $instance ) {
				$post_title   = $instance->get( 'post' )->post_title;
				$post_name    = $instance->get( 'post' )->post_name;
				$post_id = $instance->get('post')->post_id;
				$instance_id  = $instance->get( 'instance_id' );
				$content     .= '<div class="hp-event">
					<a href="ai1ec_event/'.$post_name.'/?instance_id='.$instance_id.'">'
					.$post_title.'</a><br />'.$instance_id.'<br /><a class="read-more-link"  href="ai1ec_event/'.$post_name.'/?instance_id='.$instance_id.'">read more</a>
					</div>';
		}

so I tried changing the post_id with your way get_the_post_thumbnail($post_id, 'single-post-thumbnail');
and then it show to me one image but from one normal post (not all in one event calendar) and only one image. Not one image for each event.

foreach ( $date['events']['notallday'] as $instance ) {
				$post_title   = $instance->get( 'post' )->post_title;
				$post_name    = $instance->get( 'post' )->post_name;
				$post_id = $instance->get('post')->post_id;
				$instance_id  = $instance->get( 'instance_id' );
				$content     .= '<div class="hp-event">
					<a href="ai1ec_event/'.$post_name.'/?instance_id='.$instance_id.'">'
					.$post_title.'</a><br />'.$instance_id.'<br />'.get_the_post_thumbnail($instance_id, 'single-post-thumbnail').'<a class="read-more-link"  href="ai1ec_event/'.$post_name.'/?instance_id='.$instance_id.'">read more</a>
					</div>';
		}