bp_member_add_auto_join_groups( int $user_id,  $key,  $user )

function bp_member_add_auto_join_groups( $user_id, $key, $user ) {

	$user_member_type = bp_get_member_type( $user_id );

	// Get post id of selected profile type.
	$post_id = bp_member_type_post_by_type( $user_member_type );

	// Get selected Auto Membership Approval group types.
	$group_types = get_post_meta( $post_id, '_bp_member_type_enabled_group_type_auto_join', true );

	if ( !empty( $group_types ) && isset( $group_types ) ) {

		foreach ( $group_types as $group_type ) {

			$groups_args = array(
				'object' => 'groups',
				'per_page' => 0,
				'group_type' => array( $group_type ),
			);

			if ( bp_has_groups( $groups_args ) ) :

				while ( bp_groups() ) : bp_the_group();

					$group_id = bp_get_group_id();

					// check if already member
					$membership = new BP_Groups_Member( $user_id, $group_id );
					if( !isset($membership->ID) ){
						// add as member
						groups_accept_invite($user_id, $group_id);
					}

				endwhile;

			endif;
		}
	}
}