How to send a new characteristic value from the ESP32 client to the esp32 BLE server?

[alexpe28]

I can connect to the server through the BLE scanner application and send the value to the ELEM_UUID characteristic.
And I don’t understand how to write a sketch on the ESP32 client so that he would do the same without a smartphone.
Who understands please write how to do it.
Thank you very much in advance!

Code ESP32 Server:

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1. #include <BLEDevice.h>
2. #include <BLEUtils.h>
3. #include <BLEServer.h>
4.  
5. // See the following for generating UUIDs:
6. // https://www.uuidgenerator.net/
7.  
8. #define SERVICE_UUID        "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
9. #define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8"
10.  
11. #define ELEM_UUID              "cc46b944-003e-42b6-b836-c4246b8f19a0" // ID
12.  
13. void setup() {
14.   Serial.begin(115200);
15.   Serial.println("Starting BLE work!");
16.  
17.   BLEDevice::init("Long name works now");
18.   BLEServer *pServer = BLEDevice::createServer();
19.   BLEService *pService = pServer->createService(SERVICE_UUID);
20.   BLECharacteristic *pCharacteristic = pService->createCharacteristic(
21.                                          CHARACTERISTIC_UUID,
22.                                          BLECharacteristic::PROPERTY_READ |
23.                                          BLECharacteristic::PROPERTY_WRITE
24.                                        );
25.  
26.   BLECharacteristic *pElem;
27.  
28.   class ElemCallbacs : public BLECharacteristicCallbacks {
29.   void onWrite(BLECharacteristic *pCharacteristic) {
30.       std::string value1 = pCharacteristic->getValue();
31.       Serial.println(value1.c_str());
32.   }
33. };
34.   pElem = pService->createCharacteristic(ELEM_UUID,BLECharacteristic::PROPERTY_READ| BLECharacteristic::PROPERTY_WRITE);
35.   pElem->setCallbacks(new ElemCallbacs());
36.  
37.   pCharacteristic->setValue("Hello World says Neil");
38.   pService->start();
39.   // BLEAdvertising *pAdvertising = pServer->getAdvertising();  // this still is working for backward compatibility
40.   BLEAdvertising *pAdvertising = BLEDevice::getAdvertising();
41.   pAdvertising->addServiceUUID(SERVICE_UUID);
42.   pAdvertising->setScanResponse(true);
43.   pAdvertising->setMinPreferred(0x06);  // functions that help with iPhone connections issue
44.   pAdvertising->setMinPreferred(0x12);
45.   BLEDevice::startAdvertising();
46.   Serial.println("Characteristic defined! Now you can read it in your phone!");
47. }
48.  
49. void loop() {
50.   // put your main code here, to run repeatedly:
51.  
52.   delay(2000);
53.  
54. }

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