Can't insert user in Zoho Creator with API

I have a custom app built in zoho creator where 1 field is an accounts field in Zoho CRM. I can insert into every field using xml and cURL but I can't seem to get the user right..

I get this error when trying to insert in the field "User"
Failure, Invalid column value "Test" specified

Where Test is an EXISTING account.

The strange thing is that there are 2 actual fields but 1 visible field. User is visible but User_ID is invisible.. not sure if that has to do with anything.

But that's my problem.. I can't insert an account in the zoho creator.

                            <field name="User">
                                <value>$user</value>
                            </field>