functions.php

<?php

/**
 * Display Posts - Posts to Posts support
 * @see https://displayposts.com/2019/04/15/display-connected-content-using-posts-to-posts-plugin/
 */
function be_dps_p2p( $args, $atts ) {
	if( empty( $atts['connected_type'] ) )
		return $args;

	$args['connected_type'] = esc_attr( $atts['connected_type'] );
	if( !empty( $atts['connected_items'] ) )
		$args['connected_items'] = intval( $atts['connected_items'] );
	else
		$args['connected_items'] = get_queried_object_id();

	return $args;

}
add_filter( 'display_posts_shortcode_args', 'be_dps_p2p', 10, 2 );