The component uses something called history log. It has two purposes:
- Avoid transferring data again, for example in case of timeout,
- build relations between items, for example categories/articles.
If you wish to copy again an item that already is transferred, then you must go to history log choose, the specific item id, and delete it.
If you wish to transfer a group of items (for example articles, or a table from database view etc), then go to history log, select from filter the specific group (for example com_content_content for articles or com_database_name for a specific table) and hit mass delete. It is important not to hit mass delete without choosing something with filter, because it will delete the whole history log, and then you will have problem when building relations.
After that you can transfer again something that is already transferred.
Do not hesitate to contact again with us if you need more clarifications.