Problem in attachment in Mail API

Problem in attachment in Mail API

Using Mail API I can send a mail but, when I upload a file attachment, it doesn't work. 

This is the format that I tried, 
{
    "fromAddress": "josephabdulla@gmail .com",
    "toAddress": " skyclub12@zoho.com",
    "subject": "Email - Always and Forever",
    "content": "QWERTYUIO",
    "attachments":[{
    "storeName": "646740840",
        "attachmentName": "Rating of Udhaya kumar.png",
        "attachmentPath": "/Mail/6467408401512740745391000_642421486-Rating of Udhaya kumar.png"
    }]
}

Please, provide a solution for that.