MiniZincSyntaxError on add_string() method about minizinc-python HOT 2 CLOSED

from minizinc import Instance, Model, Result, Solver, Status

gecode = Solver.lookup("gecode")
m = Model()
m.add_string(
    """
    array[1..4] of var 1..10: x;
    var int: obj;

    constraint obj = sum(x);
    output ["\\(obj)"];
    """
)
inst = Instance(gecode, m)

res: Result = inst.solve()
print(res.solution)
while res.status == Status.SATISFIED:
    with inst.branch() as child:
        child.add_string(f"constraint obj > {res['obj']};")
        res = child.solve()
        if res.solution is not None:
            print(res.solution)