Error NO_DOCUMENT_RECEIVED while sending multipart

Question

Hii have a problem while sending a documents via binary transfer in multipart requests to the endpoint: POST /restapi/v2.1/accounts/{accountId}/envelopes         Im receiving the following error:{"errorCode":"NO_DOCUMENT_RECEIVED","message":"The document element did not contain the encoded document, or there is a problem with the encoding. Bytes for document corresponding to documentId 1 not found in request. 'documentId=<x>' possibly missing from Content-Disposition header."} For some context, im sending the request from an SAP-System, and im limited to the http_interface that the system provides. I dont have full control over how the request is generated in the end and that is the problem i think:See → The content-disposition header of the added pdf-file is in lower case, while the tuturial (https://developers.docusign.com/docs/esign-rest-api/how-to/send-binary/) suggets “Content-Disposition” instead.                                                                                                                                                                                                                                As far as im aware, http-headers are case insensetive and the docusign api should be fine with this, but maybe im wrong and the problem lies therewhere else?  Thank you in advance :)