Add item to list gives : 415 - Unsupported Media Type

Hello,

I would like to add an item to a custom list using rest API.

The request gave me : Unsupported Media Type

I am using the list custom type name (SP.Data.%name%ListItem) as type in __metadata following the information here : http://msdn.microsoft.com/en-us/library/office/dn531433(v=office.15).aspx#bk_ListItem

I am able to add attachments to an existing item but i can't add a new item.

Do you have any idea?

Thanks in advance.

Regards,