Is it permissible to wear a belt for carrying expenses and papers, even if it is sewn?

There is no harm in wearing a belt over the izar (lower garment). The questioner's statement "that it is sewn" is based on a misunderstanding; what is meant by "sewn" is not something that contains stitching, but rather something that is made to fit the shape of a limb and is worn in its usual form, like a garment or trousers. If a person enters ihram wearing a patched rida' (upper garment) or izar, there is no harm in it.