Issues when use a model without id

Can you show the migration?

<?php

use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;

class CreateDomainsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('domains', function (Blueprint $table) {
            $table->string('domain')->unique();
            $table->unsignedInteger('user_id')->nullable(false)
                ->comment('Albarid for best performance with relations tables');
            $table->text('description')->nullable();
            $table->text('disclaimer')->nullable();
            $table->unsignedInteger('aliases')->nullable(false)->default(0);
            $table->unsignedInteger('mailboxes')->nullable(false)->default(0);
            $table->unsignedInteger('maillists')->nullable(false)->default(0);
            $table->unsignedInteger('quota')->nullable(false)->default(0)->comment('Real quota asigned in Mb');
            $table->unsignedInteger('max_quota')->nullable(false)->default(0)->comment('Grace quota asigned in Mb');
            $table->unsignedBigInteger('quota_used')->nullable(false)->default(0)->comment('Quota used in Bytes');
            $table->unsignedInteger('quota_user_default')->nullable(false)->default(1024)
                ->comment('QUota default mailbox in Megabytes');
            $table->string('transport')->nullable(false)->default('dovecot');
            $table->boolean('backupmx')->nullable(false)->default(false)->index();
            // $table->json('settings')->nullable();
            $table->boolean('active')->nullable(false)->default(true)->index();
            $table->timestamps();
            $table->softDeletes();
            $table->timestamp('expires_in')->nullable(true)->index();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('domains');
    }
}

Looks fine. I assume it works if you disable CascadeSoftDeletes?

A lot of thanks for your effort. After this problems, I get way for add id to tables without id, and refactor app and mother app. Is more easy for me.

Best regards.