Send string signal from combobox in qml

Fakhr

I'm trying to send a string from combobox to an api. Unfortunately nothing is being sent.

main.qml

import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.Controls 2.15
Window {
    id: mainWindow
    width: 1120
    height: 680
    visible: true

    Rectangle {
        id: mainBody
        color: "#F4F4F5"
        anchors.fill: parent

        ComboBox {
            id: comboBox
                x: 219
                y: -9
                width: 504
                height: 40
                model: [ "hp", "lenovo", "acer"]
        }
        Button {
            id: bt
            width: 24
            height: 24
            onClicked: backend.add(comboBox.text)
        }
    }
    Connections {
        target: backend
    }
}

main.py

# This Python file uses the following encoding: utf-8
import os
# from pathlib import Path
import sys
import json
import requests
from PySide2.QtWidgets import QApplication
from PySide2.QtQml import QQmlApplicationEngine
from PySide2.QtCore import Slot, Signal, QObject

class MainWindow(QObject):
    def __init__(self):
        QObject.__init__(self)

    signalcombo = Signal(str)
    @Slot(str, str, str)

    def add(self, getCombo):
        putdata1 = {"category_name": getCombo}
        data1 = 
        requests.post("random api", json=putdata1)
        print(data1.text)
if __name__ == "__main__":
    app = QApplication(sys.argv)
    engine = QQmlApplicationEngine()

    # engine.load(os.fspath(Path(__file__).resolve().parent / "qml/main.qml"))
    engine.load(os.path.join(os.path.dirname(__file__), "qml/main.qml"))

    # Get Context
    main = MainWindow()
    engine.rootContext().setContextProperty("backend", main)
    if not engine.rootObjects():
        sys.exit(-1)
    sys.exit(app.exec_())

Now the problem is that when data1.text is printed it says "Inserted Successfully", but there is nothing in the database not even blank space. No data is being sent. Can anyone help me. This approach is working for textField but not for combobox.