Upload a file to an existing message (as an attachment).

Accepts a multipart/form-data content-type request, expecting a file in its payload.
The uploaded file will be attached to the message with the provided messageId.
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 403 Error Codes (error property):

Forbidden - The user does not have sufficient access to the message that they are attempting to attach a file to.

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.

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