The API for imports supports many types of entities that you can import from the external source to YouTrack. However, there are entities that are not covered and can't be imported using this method. It's possible to import some of these entities using the YouTrack REST API and the Hub REST API .
The following entities can be imported into YouTrack with import scripts:
Custom fields and their values
The following entities can't be imported into YouTrack with import scripts:
Agile boards. To import these entities, use the YouTrack REST API.
Dashboards. To import these entities, use the Hub REST API.
For more details about imported entities, see Import API Reference.