Where can I find the winbiz-companyid ?
The parameter winbiz-companyid is part of the Headers of the API.
Every folder or company in Winbiz has an Identifier that is unique in each Winbiz installation. It is visible to the users and it is in the column "Number" when the list of the folders is opened.
In an English installation: File -> Open -> Column "N°" in the left pane
In a German installation: Datei -> Öffnen -> Column "Nr" in the left pane
In a French installation: Fichier -> Ouvrir -> Column "Nr" in the left pane
In an Italian installation: File -> Apri -> Column "Nr" in the left pane