Php 如何在 Laravel 中保存多对多

我正试着拯救很多很多人的幼体.我已经试了将近7个小时了.但还是解决不了这个问题.

以下是自定义迁移表:

public function up()
    {
        Schema::create('customer', function (Blueprint $table) {
            $table->id();
            $table->timestamps();
            $table->string("customer_phone", 255);
        });
    }

以下是我的Send_Messages迁移表:

 public function up()
    {
        Schema::create('send_messages', function (Blueprint $table) {
            $table->id();
            $table->timestamps();
            $table->unsignedBigInteger("template_id");
            $table->unsignedBigInteger("sender_number_id");
            // $table->unsignedBigInteger("cutomer_id");
            $table->foreign("template_id")->references("id")->on("messagecontent")->onDelete("cascade");
            $table->foreign("sender_number_id")->references("id")->on("sendernumber")->onDelete("cascade");
           // $table->foreign("customer_id")->references("id")->on("customer")->onDelete("cascade");

        });
    }

以下是我的数据透视表:

Schema::create('customer_send_message', function (Blueprint $table) {
    $table->id();
    $table->timestamps();
    $table->foreignId("send_messages_id")->constrained("send_messages");
    $table->foreignId("customer_id")->constrained("customer");
});

这是CustomerModel

class Customer extends Model
{
    use HasFactory;

    protected $table = "customer";

    protected $fillable = [ "customer_phone" ];

    public function sendmessage () {
        return $this->belongsToMany(SendMessage::class, "customer_send_message");
    }

}

这是我的SendMessageModel

class SendMessage extends Model
{
    use HasFactory;

    protected $table = "send_messages";

    protected $fillable = [
        "customer_id",
        "template_id",
        "sender_number_id"
    ];

    public function messageContent() {
        return $this->belongsTo(MessageContentModel::class);
    }

    public function senderNumber() {
        return $this->belongsTo(SendNumberModel::class);
    }

    public function customer() {
        return $this->belongsToMany(Customer::class, "customer_send_message");
    }

}

以下是我正在try 保存的控制器:

    public function send(Request $request) {
        $sendmessage = new SendMessage();

        $sendmessage->template_id = $request->get("template_id");
        $sendmessage->sender_number_id = $request->get("sender_number_id");


        $customers = Customer::find(1);
        $sendmessage->customer()->attach($customers);
        $sendmessage->save();
//        $send->save();
        return redirect("")->with("message", "Sms sent!");
    }

我想要获得多个数据，然后我想要保存它，就像Django许多任何字段一样.实际上，我曾经是Django的开发人员，最近我改用了laravel.我不知道那么多事情.那么有没有解决这个问题的办法呢？我只想存钱.

我在保存时出错:

SQLSTATE[42S22]:未找到列:1054‘field list’中的未知列‘Send_Message_id’

我不知道为什么我会收到这个错误！！