Html – Facing problem in transferring data in request body in login/signup form

I have made login/signup page and the corresponding routes using NodeJS. The problem i am facing is that on clicking submit button, signup route is calling but the data is not transferring in request body.
this error message is showing

{"message":"User validation failed: username: Path username is required., password: Path password is required."},
I have also run this route on postman. there everything is functioning properly. data is properly store in database.

This is the signup form.

<div id="signup-form">
        <h2>Signup</h2>
        <form method="post" action="/signup">
            <div class="form-floating mb-3">
                <input type="text" class="form-control" for="username">
                <label for="username">Username</label>
            </div>
            <div class="form-floating">
                <input type="password" class="form-control" for="password">
                <label for="password">Password</label>
            </div>

            <button type="submit" class="btn btn-primary" onclick="showLoginForm()">Signup</button>
        </form>
        <div class="instead-button">
            <button class="btn btn-primary" onclick="showLoginForm()">Login instead</button>
        </div>
    </div>

and this is backend code

app.post('/signup', async (req, res) => {
  try {
    console.log('inside');
    const { username, password } = req.body;
    const user = await User.create({ username, password });
    res.status(201);
  } catch (error) {
    res.status(400).json({ message: error.message });
  }
});