How do I solve this in android register code

Question

After logging in with email and password, the user tries to add space. When I fill out the form, an error message appears like this" <br/><b> Warning<b>: Undefined Array Key"

    import android.content.Intent;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.Button;
    import android.widget.CheckBox;
    import android.widget.EditText;
    import android.widget.Toast;
    import androidx.appcompat.app.AppCompatActivity;
    import com.android.volley.AuthFailureError;
    import com.android.volley.Request;
    import com.android.volley.Response;
    import com.android.volley.VolleyError;
    import com.android.volley.toolbox.StringRequest;
    import com.android.volley.toolbox.Volley;
    import java.util.HashMap;
    import java.util.Map;

    public class owner_addspace extends AppCompatActivity {

        private EditText titleEditText, addressEditText, postcodeEditText, costEditText;
        private CheckBox availableCheckBox;
        private Button submitButton;
       private String email, password;
   
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_owner_addspace);

            // Get user's email and password from previous activity
            Intent intent = getIntent();
            email = intent.getStringExtra("email");
            password = intent.getStringExtra("password");

            titleEditText = findViewById(R.id.editTextSpace);
            addressEditText = findViewById(R.id.editTextAddress);
            postcodeEditText = findViewById(R.id.editTextPostCode);
            costEditText = findViewById(R.id.editTextCost);
            availableCheckBox = findViewById(R.id.checkBoxIsAvailable);
            submitButton = findViewById(R.id.buttonAddSpace);
    
            submitButton.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    String title = titleEditText.getText().toString().trim();
                    String address = addressEditText.getText().toString().trim();
                    String postcode = postcodeEditText.getText().toString().trim();
                    String cost = costEditText.getText().toString().trim();
                    boolean isAvailable = availableCheckBox.isChecked();

                    // Validate the input values
                    if (title.isEmpty()) {
                        titleEditText.setError("Title is required");
                        titleEditText.requestFocus();
                          return;
                    }

                    if (address.isEmpty()) {
                        addressEditText.setError("Address is required");
                        addressEditText.requestFocus();
                        return;
                    }

                    if (postcode.isEmpty()) {
                        postcodeEditText.setError("Postcode is required");
                        postcodeEditText.requestFocus();
                        return;
                    }
   
                    if (cost.isEmpty()) {
                         costEditText.setError("Cost per hour is required");
                        costEditText.requestFocus();
                        return;
                    }

  
                    StringRequest stringRequest = new StringRequest(Request.Method.POST, Constants.URL_ADD_SPACE, new Response.Listener<String>() {
                        @Override
                        public void onResponse(String response) {
                            // Show a toast message
                            Toast.makeText(owner_addspace.this, response, Toast.LENGTH_SHORT).show();

                            // Go back to the main activity
                            finish();
                        }
                    }, new Response.ErrorListener() {
                        @Override
                        public void onErrorResponse(VolleyError error) {
                            // Show an error message
                            Toast.makeText(owner_addspace.this, "Error: " + error.getMessage(), Toast.LENGTH_SHORT).show();
                        }
                    }) {
                        @Override
                        protected Map<String, String> getParams() throws AuthFailureError {
                            Map<String, String> params = new HashMap<>();
                            params.put("ps_title", title);
                            params.put("ps_address", address);
                            params.put("postcode", postcode);
                            params.put("cost_per_hour", cost);
                            params.put("is_available", isAvailable ? "Available" : "Not Available");

                            if(email != null) {
                                params.put("email", email);
                            }
                            if(password != null) {
                                params.put("password", password);
                            }
                            return params;
                        }
                    };

                    Volley.newRequestQueue(owner_addspace.this).add(stringRequest);
                }
            });
        }
    }

php code

    <?php
   // Define database connection parameters
    $servername = "localhost";
    $username = "root";
    $password = "";
    $dbname = "mydb";

    // Create database connection
    $conn = new mysqli($servername, $username, $password, $dbname);

    // Check for connection errors
    if ($conn->connect_error) {
        die("Connection failed: " . $conn->connect_error);
    }

    // Get the input values from the form
    $ps_title = $_POST['ps_title'];
    $ps_address = $_POST['ps_address'];
    $postcode = $_POST['postcode'];
    $cost_per_hour = $_POST['cost_per_hour'];
    $is_available = isset($_POST['is_available']) ? "Available" : "Not 
    Available";
    $email = $_POST['email'];
    $password = $_POST['password'];

     // Check if the postcode already exists in the postcode table
    $result = $conn->query("SELECT PostcodeID FROM postcode WHERE Postcode = 
    '$postcode'");

    if ($result->num_rows > 0) {
        // The postcode already exists, get the PostcodeID
        $row = $result->fetch_assoc();
        $postcode_id = $row['PostcodeID'];
    } else {
        // The postcode does not exist, add it to the postcode table and get 
    the PostcodeID
        $conn->query("INSERT INTO postcode (Postcode) VALUES 
    ('$postcode')");
        $postcode_id = $conn->insert_id;
    
        // Use the Google Maps API to get the geolocation data of the postcode
        $geocode_url = "https://maps.googleapis.com/maps/api/geocode/json?address=$postcode&key=AIzaSyB0wJammsFsGqsX5X0s97U10oj_s5_jgM8";
        $geocode_data = json_decode(file_get_contents($geocode_url));
    
        if ($geocode_data->status == "OK") {
            $latitude = $geocode_data->results[0]->geometry->location->lat;
            $longitude = $geocode_data->results[0]->geometry->location->lng;
            $conn->query("UPDATE postcode SET Latitude = '$latitude', Longitude = '$longitude' WHERE PostcodeID = '$postcode_id'");
        }
    }

    // Get the H_ID from the households table using the email and password
    $result = $conn->query("SELECT H_ID FROM households WHERE H_Email = 
    '$email' AND H_Password = '$password'");

    if ($result->num_rows > 0) {
        $row = $result->fetch_assoc();
        $h_id = $row['H_ID'];
    
        // Insert the parking space into the parkingspace table
        $conn->query("INSERT INTO parkingspace (PS_Title, PS_Address, 
    PostcodeID, H_ID, PS_Cost, PS_Status) VALUES ('$ps_title', 
    '$ps_address', '$postcode_id', '$h_id', '$cost_per_hour', 
    '$is_available', '')");
    
        echo "Parking space added successfully!";
    } else {
        echo "Invalid email or password.";
    }

    // Close the database connection
    $conn->close();
    ?>

when user logged, try to add car space. after filling form and click update button error comes like this
Warning:Undefined Array Key