Laravel5.7 : how to store nested arrays to database

Using Laravel 5.7.
Designing an app with many views containing forms.
In this view:
- there is one (only one) client_id field. This is hidden and the value is retrieved from an url segment.
- other fields are dynamic (date, type, comments) and refers to one or more products bought by this client.
I cannot figure out how to save input values from the dynamic fieds to the database (sorry, I am quite new to coding) See below my current code and attempts. I found related answers in stack overflow could not make them fit to my case. I would appreciate help

STORE() FUNCTION IN CONTROLLER

public function storeDYNarray(Request $request)
    {
        $client = $request->input('client_id');
        $all = $request->input();
        $products = $request->input('product');
        //dd($all); SEE BELOW

//THIS CREATES AS MANY NEW ENTRIES IN PRODUCTS TABLE AS NEEDED WITH THE CORRESPONDING client_ID
        foreach ($products as $product){
            $dia = new Product;
            //client_id is retrieved from an URL segment
            $dia->client_id = $request->input('client_id');
//DON'T KNOW HOW TO SAVE VALUES FROM THE DYNAMIC FIELDS
            $dia->save();
    }

return dd($all); OUTPUT

array:3 [▼
  "_token" => "uvtLaCiuAueBIuyWkoCoOTdQzYB1paxhnLw0lbyO"
  "client_id" => "898"
  "product" => array:2 [▼
    1 => array:3 [▼
      "date" => "2019-03-13"
      "type" => "new"
      "comment" => "surplus"
    ]
    2 => array:3 [▼
      "date" => "2019-03-28"
      "type" => "used"
      "comment" => "good condition"
    ]
  ]
]

I tried strategies along those lines...I kind of see what does not make sense but cannot do better:

foreach ($products as $product){
            $dia = new product;
            $dia->client_id = $request->input('client_id');
                foreach ($product as $key=>$value){
                    $dia->product_date = $request->input('date'); //or input('*.date'); 
                    $dia->product_type = $request->input('type'); //or input('*.type');
                    $dia->product_comment = $request->input('comment'); //or input('*.comment');
                }
            $dia->save();
    }
    //for the second loop, I also tried using a $i variable and to retrieve values with $product[$i][date]...


$client_products = array();
        foreach ($products as $product)
        {
            $client_products[] = new product(array(
                'client_id' => $client,
                'product_date' => $product['date'],
                'product_type' => $product['type'],
                'comment_about_product' => $product['comment'],
            ));
        }
        $client->products()->saveMany($client_products);

PRODUCTS TABLE

class CreateProductsTable extends Migration
{
    public function up()
    {
        //KEPT VALIDATION PARAMETERS SIMPLE FOR KNOW
        Schema::create('products', function (Blueprint $table) {
            $table->increments('product_id');
            $table->string('client_id')->nullable($value = true); 
            $table->date('product_date')->nullable($value = true);
            $table->string('product_type')->nullable($value = true);
            $table->longText('comment_about_product')->nullable($value = true);
            $table->timestamps();
        });
    }

PRODUCT MODEL

class product extends Model
{
    //GIVEN THE STRUCTURE OF ARRAYS WHEN dd($all); I DONT THINK I NEED THAT
    /*
    public $fillable = [
        'client_id',
        'product_date',
        'product_type',
        'comment_about_product_type', 
    ];
    */

    public function client(){
        return $this->belongsTo('App\client');
        }
}

CLIENT TABLE

<?php
//use Illuminate...
class CreateclientsTable extends Migration
{ 
    public function up()
    {
        Schema::create('clients', function (Blueprint $table) {
            $table->string('client_id');
            $table->primary('client_id');
            //other columns...
            $table->integer('user_id')->nullable($value = true);
            $table->timestamps();
        });
    }

CLIENT MODEL

class client extends Model
{
    protected $primaryKey = 'client_id';
    public $incrementing = false;
    protected $keyType = 'string';

    public function user(){
        return $this->belongsTo('App\User');
        }

    public function products(){
        return $this->hasMany('App\product');
        }
}

via Chebli Mohamed