I have graphql syntax error from BuildSchema

I use nodejs with typescript for my project and I decided to use graphql but I have a problem I tried many things but I am still in one place when I tried to debug the problem I found that this error occurs when I use "BuildSchema" from "graphql" package.

so I give you detail and I hope you will help me

error description:

return new _GraphQLError.GraphQLError("Syntax Error: ".concat(description), undefined, source, [position]);
         ^
GraphQLError [Object]: Syntax Error: Expected Name, found "}".

my server.ts code:

    import express from "express";
import bodyParser from "body-parser";
import cors from "cors";
import { connect } from "mongoose";
import { graphqlHTTP } from "express-graphql";
import { GraphQLSchema, buildSchema } from "graphql";

const app = express();

// ======= Env Configuration
import { config } from "dotenv";
config();

// ====== app middleware
app.use(bodyParser.json());
app.use(cors());

// ============= Graphql ============== \
import resolver from "./graphql/resolver";
import schema from "./graphql/schema";

const ss = buildSchema(schema);

app.use(
  "/graphql",
  graphqlHTTP({
    graphiql: true,
    schema: ss,
    rootValue: resolver,
  })
);

// ============ Connect to Server / Mongodb
const PORT = 5000;

connect(`${process.env.MONGO_URL}`)
  .then(() => {
    console.log(`mongoose connected...`);
    app.listen(PORT, () => {
      console.log(`server connected on ${PORT} port...`);
    });
  })
  .catch((error) => {
    throw error;
  });

here is main schema file:

import { buildSchema, GraphQLSchema } from "graphql";

// ========== Schemas
import { UserSchema, UserRootQuery, UserRootMutation } from "./user.schema";

const Schema = `
    ${UserSchema}

    type RootQuery {
        ${UserRootQuery}
    }

    type RootMutation {
        ${UserRootMutation}
    }

    schema {
        query: RootQuery
        mutation: RootMutation
    }
`;

export default Schema;

here is one of the schema file:

export const UserSchema = `
    type User {
        userName: String!
        age: Init!
        country: String!
        gender: String!
    }
`;

export const UserRootQuery = `
    users(userId: String): User
`;

export const UserRootMutation = `

`;