Accepts a multipart/form-data content-type request, expecting a file in its payload.
A new message will be created containing this file as its first attachment.
This endpoint cannot be tested in Swagger, and requires actual implementation into an application.

HTTP Status Code 400 Error Codes (error property):

InvalidMessageId - An invalid message id was provided.

HTTP Status Code 401 Error Codes (error property):

Unauthorized - An Authorization token was not provided and is required.

AccessTokenInvalid - The access token is expired or invalid.

HTTP Status Code 413 Error Codes (error property):

FileTooLarge - The file is too large to upload.

DailyUserFileTransferUsageExceeded - The user's daily file transfer usage has been exceeded.

HourlyUserFileTransferUsageExceeded - The user's hourly file transfer usage has been exceeded.

DailyCompanyFileTransferUsageExceeded - The daily company file transfer usage has been exceeded.

HourlyCompanyFileTransferUsageExceeded - The hourly company file transfer usage has been exceeded.