Cannot open Camera An error occurred while connecting to camera: 0

I started developping an app and I need to use the camera of my phone, and when I use the method Camera.open(), either with cameraId or not, it returns the error "An error occurred while connecting to camera: 0". My AndroidManifest.xml is:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.telecombretagne.holowater">

    <uses-permission android:name="android.permission.CAMERA"/>
    <uses-feature android:name="android.hardware.camera" />
    <uses-feature android:name="android.hardware.autofocus" />
    <uses-feature android:name="android.hardware.flash" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".camera"
            android:label="@string/title_activity_camera"
            android:theme="@style/AppTheme.NoActionBar"></activity>
    </application>

</manifest>

My phone's Android Version is 6.0.1, and it's a BQ Aquaris M5.

Thanks in advance.