ESP32 Bluetooth Master does not connect

Question

I want to connect an ESP32 to a SMA Sunny Boy SB5000-TL Solar convertor over Bluetooth, but I cannot establish a connection and I'm kind of stuck. I use the internal bluetooth module of the ESP32.

What I've done:

• I started with this project: https://github.com/delhatch/ESP32_to_SMA but I did not get past the connection. I tried to locate the problem area:

• I tried using an Android app (Oxley Solar) to connect to the SB5000-TL Solar convertor, and that works great. The pin code of the convertor is set to 0000.

• I tried using two ESP32 modules, one as master, one as slave and that works as well, though I do not need to set a pin. So the bluetooth module of my ESP32 works properly.

So the problem must be in my code, I guess.

This is the code I use to connect to the convertor:

#include "BluetoothSerial.h"
#if !defined(CONFIG_BT_ENABLED) || !defined(CONFIG_BLUEDROID_ENABLED)
#error Bluetooth is not enabled! Please run make menuconfig to and enable it
#endif
BluetoothSerial SerialBT;
boolean confirmRequestPending = true;
// uint8_t ESP32Slave[6]  = {0x84, 0xCC, 0xA8, 0x2C, 0x70, 0x1E}; // Address of Slave.
uint8_t SMA[6]  = {0x00, 0x40, 0x65, 0x12, 0x4B, 0x3E}; // Address of my SMA inverter.
const char *pin = "0000"; //<- standard pin
void setup() {
  Serial.begin(115200);
  SerialBT.enableSSP();
  SerialBT.onConfirmRequest(BTConfirmRequestCallback);
  SerialBT.onAuthComplete(BTAuthCompleteCallback);
  SerialBT.begin("ESP32master", true); //Bluetooth device name
  SerialBT.register_callback(callback);
  SerialBT.setPin("0000");
  Serial.println("Connecting...");
  bool connected = SerialBT.connect(SMA);
  if (connected) {
    Serial.println("Connected!");
  } else {
    Serial.println("NOT Connected!");
  }
  delay(500);
  SerialBT.end();
  Serial.println("Bye!");
}
void loop() {
}
void callback(esp_spp_cb_event_t event, esp_spp_cb_param_t *param) {
  Serial.print("Got event!");  Serial.println(event);
}
void BTConfirmRequestCallback(uint32_t numVal)
{
  confirmRequestPending = true;
  Serial.println(numVal);
}
void BTAuthCompleteCallback(boolean success)
{
  confirmRequestPending = false;
  if (success)
  {
    Serial.println("Pairing success!!");
  }
  else
  {
    Serial.println("Pairing failed, rejected by user!!");
  }
}

This is the result in the Serial console:

Connecting...
Got event!0
Got event!8
NOT Connected!
Got event!1
Bye!

I tried to replace the Mac Address with the name of the Convertor, I tried with and without pin.

I'm kind of stuck. Any idea's of how I can check what is wrong?

Is there any kind of scanner I can use to see what is happening with the app that works and what is (not) happening with my code?

Other ways to get more info/leads?
Could I use a Bluetooth sniffer or so (no experience) to find out what happens?

Any advice would be greatly appreciated!