Answer
Double-check the exact spelling and formatting of the content-disposition header name — it needs to be X-IFS-Content-Disposition (with the hyphens between 'IFS,' 'Content,' and 'Disposition'), not a variant like X-IFS-ContentDisposition without the internal hyphen. A header name that doesn't match exactly won't be recognized by the endpoint and produces this same generic internal-server-error response rather than a clearer header-related error message.