Provide the following details to create an attachment for a given email template ID:

• Name (string, *required): The name of the file. This field is required, and if it contains a null value in the request, the API returns an error.
• MimeType (string, *required): A string sent along with a file indicating the type of the file (describing the content format, for example, a sound file might be labeled audio/ogg, or an image file image/png). This field is required, and if it contains an invalid or null value in the request, the API returns an error. For more information on supported media types, click here.
• File [Obsolete] (string, *required): It is recommended to use 'FileContent' for all the attachments (especially large files). FileData is a Base64 encoded string of your file. Out of FileData and FileContent, either of the fields is required, and if it contains an invalid or null value in the request, the API returns an error.
• FileContent (byte[], *required): Byte array collection of your file. Out of FileContent and FileData, either of the fields is required, and if it contains an invalid or null value in the request, the API returns an error.