addProjectDependence

result_type
CTaskItem::addProjectDependence(
 array $parentId,
 $linkType = DependenceTable::LINK_TYPE_FINISH_START
);

Adds a dependency from one task to another within Gantt.

Parameter	Description
parentId	INT. Task with added dependency
linkType	INT type of link. Default: 2. Changes from 0 to 3 depending on which type of link is required.

$task = CTaskItem::getInstance(1, 1);
$task->addProjectDependence(2, \Bitrix\Tasks\Task\DependenceTable::LINK_TYPE_FINISH_FINISH)