bp_invites_member_invite_activate_user( $user_id,  $key,  $user )

function bp_invites_member_invite_activate_user( $user_id, $key, $user ) {
	global $bp;

	$email = bp_core_get_user_email( $user_id );

	$inviters 	= array();

	$args = array(
		'post_type'  => bp_get_invite_post_type(),
		'posts_per_page' => -1,
		'meta_query' => array(
			array(
				'key'     => '_bp_invitee_email',
				'value'   => $email,
				'compare' => '=',
			),
		),
	);

	$bp_get_invitee_email = new WP_Query( $args );

	if ( $bp_get_invitee_email->have_posts() ) {

		// From the posts returned by the query, get a list of unique inviters
		while ( $bp_get_invitee_email->have_posts() ) {
			$bp_get_invitee_email->the_post();

			$inviter_id	= get_the_author_meta( 'ID' );
			$inviters[] 	= $inviter_id;

			// Mark as accepted
			update_post_meta( get_the_ID(), '_bp_invitee_status', 1 );
			update_post_meta( get_the_ID(), '_bp_invitee_registered_date', date( 'Y-m-d H:i:s' ) );

			$member_type = get_post_meta( get_the_ID(), '_bp_invitee_member_type', true );
			if ( isset( $member_type ) && !empty( $member_type ) ) {
				bp_set_member_type( $user_id, '' );
				bp_set_member_type( $user_id, $member_type );
			}
		}

	}

}