I am trying to render my terrain using an EBO, but the function glDrawElements returns an error (1282). I tried to find out what is causing the error, but everything seems to be as it should according to my understanding.

In my ResourceManager class I load the heightmap and create the EBO and VBO.

std::shared_ptr<Terrain> ResourceManager::LoadTerrain(const std::string& filePath)
{
    int nrChannels;
    unsigned int vertexCount;
    int width;
    int length;
    float w = 10.0f, l = 10.0f;
    unsigned char* data = stbi_load(filePath.c_str(),&width, &length,&nrChannels,0);
    std::vector<glm::vec3> vertices(width * length);
    std::vector<unsigned int> triangles;

    if (data == NULL)
    {
        std::cout << "Cannot load the heightmap!" << std::endl;
    }

    for (int z = 0; z < length; z++)
    {
        for (int x = 0; x < width; x++)
        {
            // normalizing the x and z of the vector
            glm::vec3 vertex = glm::vec3(x/(float)width,0,z/(float)length);

            // multiplying by the width and length
            vertex.x *= w;
            vertex.z *= l;
            // shifting the center to be in the center of the object.
            vertex.x -= width/2;
            vertex.z -= length/2;

            vertices[vertexCount] = vertex;

            // unsigned char* pixelOffset = data + (z + this->length * x) * nrChannels;
            // std::cout << "red " << static_cast<unsigned int>(pixelOffset[0]) << std::endl;
        
            if ((vertexCount+1 % width) != 0 && z+1 < length)
            {
                triangles.push_back(vertexCount);
                triangles.push_back(vertexCount + width);
                triangles.push_back(vertexCount + width + 1);

                triangles.push_back(vertexCount);
                triangles.push_back(vertexCount + width + 1);
                triangles.push_back(vertexCount + 1);
            }
            vertexCount++;
        }
    }    
    stbi_image_free(data);

    // OPENGL Part
    GLuint IBO, VBO;
    glGenBuffers(1, &VBO);
    glBindBuffer(GL_ARRAY_BUFFER,VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(glm::vec3) * vertices.size(), vertices.data(), GL_STATIC_DRAW);

    glGenBuffers(1, &IBO);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,IBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(unsigned int) * triangles.size(), triangles.data(), GL_STATIC_DRAW);

    std::shared_ptr<Terrain> terrain = std::make_shared<Terrain>(Terrain(VBO, IBO, triangles.size(), Transform()));
    terrain->transform.SetScale(glm::vec3(1.0f,1.0f,1.0f));
    terrain->transform.SetPosition(glm::vec3(0.0f,0.0f,0.0f));
    for (int i = 0; i < triangles.size(); i++)
    {
        std::cout << triangles[i] << std::endl;
    }
    return terrain;
}

The part of the code that generates the error is the following

void Terrain::Render()
{
    this->Bind();
    glDrawElements(GL_TRIANGLES,this->indexCount, GL_UNSIGNED_INT, (void*)0);
    std::cout << "after render but before unbind " << glGetError()<< " " << this->indexCount << std::endl;
    this->Unbind();
}

Bind and Unbind are just 2 GL calls.

void Terrain::Bind()
{
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, this->indexBuffer);
}

void Terrain::Unbind()
{
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
}