Ionic 4 not print in thermal bluetooth

Question

I tried to print text in a thermal printer "https://www.amazon.it/gp/product/B096KQ99K1/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1" but nothing appens. I uded a plugin ble Bluetooth Low Energy. The connection ok, list device ok and other method ok and write method return "OK". But don't print nothing. What Can I solve? This is my code: - details page .ts detailsPage.html

import { Component, OnInit, NgZone } from '@angular/core';
import {AlertController, LoadingController, ToastController} from '@ionic/angular';
import { ActivatedRoute, Router } from '@angular/router';
import { BLE } from '@awesome-cordova-plugins/ble/ngx';
  
// Bluetooth UUIDs
let BLE_SERVICE = ''; //= '180A';
let BLE_CHARACTERISTIC = ''; // '2A29';


@Component({
  selector: 'app-details',
  templateUrl: './details.page.html',
  styleUrls: ['./details.page.scss']

})
export class DetailsPage implements OnInit {

  dispositivo;
  peripheral: any = {};
  statusMessage: string;
  public dataFromDevice: any;

  constructor(public route: ActivatedRoute,
              public router: Router,
              private ble: BLE,
              private toastCtrl: ToastController,
              private alertCtrl: AlertController,
              private loadingCtrl: LoadingController,
              private ngZone: NgZone) {

    this.route.queryParams.subscribe(params => {
      if (params && params.special) {
        const device = JSON.parse(params.special);
        this.dispositivo = device;
      }
    });
  }

  async presentLoadingText(macAddress) {
    await this.loadingCtrl.create({
      message: 'Please wait...'
    }).then((res) => {
      res.present();
    });
    this.bleConnect(this.dispositivo);
  }

  bleConnect(device) {
    this.ble.connect(device.id).subscribe(
      peripheral => this.onConnected(peripheral),
      peripheral => this.onDeviceDisconnected(peripheral)
    );
  }

  bleDisconnect() {
    this.ble.disconnect(this.peripheral.id).then(
      () => console.log('Disconnected ' + JSON.stringify(this.peripheral)),
      () => console.log('ERROR disconnecting ' + JSON.stringify(this.peripheral)));
  }
 
  bleWrite() {
    const inputdata = new Uint8Array(3);
    inputdata[0] = 0x53; // S
    inputdata[1] = 0x54; // T
    inputdata[2] = 0x0a; // LF
   
    this.ble
      .write(
        this.peripheral.id,
        BLE_SERVICE,
        BLE_CHARACTERISTIC,
        inputdata.buffer
      )
      .then(
        (data) => {
          this.subscribe();
        },
        err => {
          console.log(err);
        }
      );
  }

  subscribe() {
    console.log('Entro?');
    this.ble
      .startNotification(this.dispositivo.id, "fff0", "fff2")
      .subscribe(
        (data) => {
           this.onValueChange(data);              
        },
        (err) =>
          this.showAlert(
            'Unexpected Error',
            err
          ).then(() =>{
            this.bleDisconnect();
          }),
      );
  }

  onValueChange(buffer: ArrayBuffer) {
  console.log('Che fa sto metodo?');
    this.ngZone.run(() => {
      try {
        if (this.dataFromDevice === undefined){
          console.log('Dati indefiniti?');
          this.dataFromDevice = this.bytesToString(buffer).replace(/\s+/g, ' ');
        } else {
          console.log('Dati DEFINITI? ' +this.dataFromDevice);
          this.dataFromDevice += '<br />' + this.bytesToString(buffer).replace(/\s+/g, ' ');
        }
      } catch (e) {
        console.log(e);
      }
    });
  }

  bytesToString(buffer) {
    return String.fromCharCode.apply(null, new Uint8Array(buffer));
  }

  onConnected(peripheral) {
    this.loadingCtrl.dismiss();
    this.ngZone.run(() => {
      this.setStatus('');
      this.peripheral = peripheral;
      const characteristics = peripheral.characteristics;
      BLE_SERVICE = characteristics[5].service;
      BLE_CHARACTERISTIC = characteristics[5].characteristic;
      this.bleWrite();
    });
  }

  async onDeviceDisconnected(peripheral) {
    const toast = await this.toastCtrl.create({
      message: 'The peripheral unexpectedly disconnected',
      duration: 3000,
      position: 'middle'
    });
    toast.present();
  }

  setStatus(message) {
    console.log(message);
    this.ngZone.run(() => {
      this.statusMessage = message;
    });
  }

  async showAlert(title, message) {
    const alert = await this.alertCtrl.create({
      header: title,
      message: message,
      buttons: ['OK']
    });
    alert.present();
  }

  // ASCII only
  stringToBytes(str) {
    const array = new Uint8Array(str.length);
    let i;
    let l;
    for (i = 0, l = str.length; i < l; i++) {
      array[i] = str.charCodeAt(i);
    }
    return array.buffer;
  }

}

HTML
<ion-header>
  <ion-toolbar>
    <ion-title>{{ peripheral.name || 'Device' }}</ion-title>
  </ion-toolbar>
</ion-header>

<ion-content class="padding">

  <ion-card>
    <ion-card-header>
      {{ dispositivo.name || 'Unnamed' }}
    </ion-card-header>
    <ion-card-content (click)="connectToBluetoothPrinter(dispositivo.id)">
      {{ dispositivo.id }}
    </ion-card-content>
  </ion-card>

</ion-content>