Move files via API

Who can help me to move billing and quotation files from sevdesk.de to billomat.de.
I want to change the Billing Cloud Software and there is no way to import the bills and quotations.
The API Docs are here:
Sevdesk: https://my.sevdesk.de/api/InvoiceAPI/doc.html
Billomat: https://www.billomat.com/api/

If you need more information, please feel free to contact me.
best regards, Timur Ut