To save a PDF, use a PUT request:
PUT https://demo.flexibee.eu/c/demo/faktura-prijata/1/prilohy/new/Faktura-PF1_0001_2020.pdf -H "Content-Type: application/pdf" -T Faktura-PF1_0001_2020.pdf
How to save a PDF to a document via API?
Attaching a PDF to an Invoice Using cURL
Written by Petr Pech