func (s *Service) GetDelegateBalance(ctx context.Context, chainID string, blockID string, pkh string) (*big.Int, error) {
    u := "/chains/" + chainID + "/blocks/" + blockID + "/context/delegates/" + pkh + "/balance"
    req, err := s.Client.NewRequest(ctx, http.MethodGet, u, nil)
    if err != nil {
        return nil, err