I'm trying to create a simple list item with the rest api on Sharepoint 2013.
My code:

$.ajax({

    url: siteUrl + /_api/web/lists/getByTitle('internal_Listname')/items,

    type: POST,

    contentType: application/json;odata=verbose,

    data: JSON.stringify({

         '__metadata': {

            'type': 'SP.Data.internal_ListnameListItem',

         },

         'K1F1': k1f1Result,

    }),

    headers: {

        accept: application/json;odata=verbose,

        X-RequestDigest: $(#__REQUESTDIGEST).val(),

    },

    success: function (data) {

        console.log(done);

    },

    error: function (err) {

        console.log(JSON.stringify(err));

    }

});

When trying to send the data I get the 403 Forbidden error.

error:{

   code:-2130575251, Microsoft.SharePoint.SPException,

   message:{

        lang:en-US,

        value:The security validation for this page is invalid and might be corrupted. Please use your web browser's Back button to try your operation again.

    }

}

• I have full admin privileges on this site and the list.