Convert JNI Java byte [] to C ++ bytearray returning 0

I have a really big problem here. I try to transfer byte [] from Java to C ++, and after conversion I get negative values. I identified a problem with unique characters in the Java [] byte, which after conversion and logging are either 0 or negative.

I tried using test byte [] for string characters, and it works fine.

Here is my code if it helps.

Java

public static native void SendMessage(byte[] message, int size); //size = message.length

C ++

static void SendMessage(JNIEnv *env, jclass cls, jbyteArray array, jint array_length)
 {
     jbyte* content_array = (env)->GetByteArrayElements(array,NULL);
     //*env->GetByteArrayRegion(array,0,array_length,content_array); //tried this as well, same results
     LOGD("content:\n"); 
     for (int i=0; i < array_length; i++) 
     {
         LOGD("%d",content_array[i]); 
     } 

     //EDIT
     SendMessage(client, (uint8_t*)content_array, array_length); //<- could the problem be at the point where I convert it to uint8_t?

      (env)->ReleaseByteArrayElements(array,content_array,0); 
  }

Output

content: 48
content: 23
content: 13
content: 56
content: 0 // <--- the problem starts here
content: -122
content: 0
content: 78
content: 32
content: -28
etc...
..
..

Now, using a simple test byte [] Java

String test = "ABC";
byte[] message = test.getBytes();
public static native void SendMessage(byte[] message, int size); //size = message.length 

C ++

static void SendMessage(JNIEnv *env, jclass cls, jbyteArray array, jint array_length)
 {
     jbyte* content_array = (env)->GetByteArrayElements(array,NULL);
    //*env->GetByteArrayRegion(array,0,array_length,content_array); //tried this as well, same results
    LOGD("content:\n"); 
    for (int i=0; i < array_length; i++) 
    {
        LOGD("%d",content_array[i]); 
      } 
      (env)->ReleaseByteArrayElements(array,content_array,0); 
  }

Output

content: 65 //this works perfectly
content: 66
content: 67

Thank you for your help. Very much appreciated.