How are your tables set up? Does your groups table have a column called role_id?

Hi Ftiersch , thanks for your reply, here are my migrations.

Groups Migration

public function up()
    {
        Schema::create('grupos', function (Blueprint $table) {
            $table->increments('id');
            $table->string('name');
            $table->string('slug');
            $table->integer('role_id')->unsigned();
            $table->foreign('role_id')->references('id')->on('roles');
            $table->timestamps();
        });
    }

Roles Migration

public function up()
    {
        Schema::create('roles', function (Blueprint $table) {
            $table->increments('id');
            $table->string('name');
            $table->string('slug');
            $table->timestamps();
        });
    }