JNI Unable to call CallVoidMethod - java-native-interface

Question

I have a requirement to make a call from C++ to Java using JNI and invoke a void method in MainActivity.
I do not have the JavaVM argument to pass to the JNI layer in this case. So I am using env->NewGlobalRef like below and retriving it by (g_javaVM)->AttachCurrentThread(&env, NULL)
I am getting an error while trying to invoke CallVoidMethod as jobject service = env->NewObject(jobj, ctor) results in NULL service.
Can you please let me know what I am missing here?
JavaVM* g_javaVM = nullptr;
jclass cls;
jclass jobj;
jint JNI_OnLoad( JavaVM* vm, void* reserved ) {
JNIEnv* env;
if( vm->GetEnv( reinterpret_cast<void**>( &env ), JNI_VERSION_1_6 ) != JNI_OK ) {
return -1;
}
cls = env->FindClass("com/test/MainActivity");
jobj = (jclass)env->NewGlobalRef(cls);
g_javaVM = vm;
return JNI_VERSION_1_6;
}
void NativeLib::play() {
JNIEnv *env;
jint rs = (g_javaVM)->AttachCurrentThread(&env, NULL);
assert(rs == JNI_OK);
jmethodID ctor = env->GetMethodID(jobj, "<init>", "()V");
jmethodID jobj_play= env->GetMethodID(jobj,"play","()V");
jobject service = env->NewObject(jobj, ctor); //Getting error on this line. service is NULL
env->CallVoidMethod(service, jobj_play);
}