Unfortunately, the REST API for the bill of materials is not documented.
Import is supported, but it is not documented and we do not recommend using it.
Bill of materials call: https://{server}/c/{idFirmy}/kusovnik/(otecCenik='code:POLOZKA').xml?detail=full
Other useful URLs where you can find additional fields and the bill of materials structure:
https://demo.flexibee.eu/c/demo/kusovnik.xml?detail=full
https://demo.flexibee.eu/c/demo/kusovnik/properties