my app is taking localhost:3000 as the server. but i have localhost:4000 as the server

My problem is that iam using axios to communicate with backend.axios had done perfect job till now. but when i wrote a code for register, my console says that
POST http://localhost:3000/api/v1/register 500 (Internal Server Error)

so till now it responded very good.but now it thrwing an error like this.

userAction.js :

export const register = (userData) => async (dispatch) => {
  try {
    dispatch({ type: REGISTER_USER_REQUEST });

    const config = { headers: { "Content-Type": "multipart/form-data" } };

    const { data } = await axios.post("/api/v1/register", userData, config);

    dispatch({ type: REGISTER_USER_SUCCESS, payload: data.user });
  } catch (error) {
    dispatch({
      type: REGISTER_USER_FAIL,
      payload: error.response.data.message,
    });
  }
};

iam using localhost:4000 as server. but it showing me localhost:3000 which means my app url

>Solution :

Because you did not specify the host in your post url.Then it may be work.

/api/v1/register => http://localhost/api/v1/register

The if you have cors issue add this to the nodejs backend app.js file (as you using nodejs):

const cors = require('cors');

app.use(cors())