INVALID DATA when Create Record

INVALID DATA when Create Record

I have a form to create new deals with a lookup multiselect´s field in other form. The field looking up is Contact_Name

The script for submission is:
for each alum in Lista_Alumnos
{
var_map = Map();
var_map = {
"Contact_Name":Nuevo_Alumno[ID == alum.ID],
"crmnmoodle__Course_Name":input.Curso,
"crmnmoodle__Enrol_Status":input.Estado,
"Deal_Name":input.tipo_de_matricula,
"Closing_Date":input.Fecha_Matriculacionn};
response = zoho.crm.createRecord("Deals",var_map);
}
info response;

The error message Is:

{"code":"INVALID_DATA","details":{"expected_data_type":"bigint","api_name":"Contact_Name"},"message":"invalid data","status":"error"}


What am I doing wrong??