Array to string conversion in Laravel

You are getting an array but expect a string. Cannot say more without the actual code

function in controller

        public function submitStudent(CreateStudentRequest $request): RedirectResponse
{

   $user = auth()->user();

   Student::create([
       'first_name' => $request->first_name,
       'last_name' => $request->last_name,
       'balances' => []
   ]);

      return redirect()->route('parent.create-student_submit', ['user_id' => auth()->user()->id]);
   }

custom request

 class CreateStudentRequest extends FormRequest
  {  
          public function authorize()
      {
         return true;
      }


public function rules()
{
    return [
        'last_name'      => 'required',
        'first_name'     => 'required',
        'country'        => 'required',
        'street_address' => 'required',
        'city'           => 'required',
        'state'          => 'required',
        'zip'            => 'required',
    ];
}

}

ROUTE

   Route::post('/parent/create-student/{user_id}', [ParentController::class, 'submitStudent'])->name('parent.create-student_submit');

VIEW

  <form id="form" method="POST" action="{{route('parent.create-student_submit', ['user_id' => $user_id])}}" class="mt-8 space-y-6 w-full">
        @csrf
        <div class="bg-white p-8">
            <div>
                <h3 class="text-lg font-medium leading-6 text-gray-900">Personal Information</h3>
                <p class="mt-1 text-sm text-gray-500">Use a permanent address where you can receive mail.</p>
            </div>
            <div class="mt-6 grid grid-cols-1 gap-y-6 gap-x-4 sm:grid-cols-6">
                <div class="sm:col-span-2">
                    <label for="last-name" class="block text-sm font-medium text-gray-700">Last name</label>
                    <div class="mt-1">
                        <input type="text" value="{{old('last_name')}}" required name="last_name" id="last_name" autocomplete="given-name" class="block w-full rounded-md border-gray-300 shadow-sm focus:border-indigo-500 focus:ring-indigo-500 sm:text-sm">
                    </div>
                </div>

                <div class="sm:col-span-2">
                    <label for="first-name" class="block text-sm font-medium text-gray-700">First name</label>
                    <div class="mt-1">
                        <input type="text" value="{{old('first_name')}}" required name="first_name" id="first_name" autocomplete="family-name" class="block w-full rounded-md border-gray-300 shadow-sm focus:border-indigo-500 focus:ring-indigo-500 sm:text-sm">
                    </div>
                </div>
                <div class="sm:col-span-2">
                    <label for="middle-name" class="block text-sm font-medium text-gray-700">Middle name</label>
                    <div class="mt-1">
                        <input type="text" value="{{old('middle_name')}}" name="middle_name" id="middle_name" autocomplete="additional-name" class="block w-full rounded-md border-gray-300 shadow-sm focus:border-indigo-500 focus:ring-indigo-500 sm:text-sm">
                    </div>
                </div>

(i did not copied all view, because i dont think something iis in view, just to showcase)

! MIGRATION (user)!

     return new class() extends Migration {
/**
 * Run the migrations.
 *
 * @return void
 */
public function up()
{
	Schema::create('users', function (Blueprint $table) {
		$table->id();
		$table->string('first_name')->default('unfilled');
		$table->string('last_name')->default('unfilled');
		$table->string('middle_name')->nullable();
		$table->string('email')->unique();
		$table->string('password');
		$table->foreignId('school_id')->default(1)->constrained();
		$table->integer('billingo_id')->default(0);
		$table->tinyInteger('summary_frequency')->default(0);
		$table->tinyInteger('finished_onboarding')->default(0);
		$table->json('user_information')->nullable();
		$table->string('two_factor_token')->nullable()->unique();
		$table->boolean('is_verified')->default(false);
		$table->rememberToken();
		$table->timestamps();
	});
}

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

};

!! MIGRATION !! (student)

     return new class extends Migration
     {
      public function up()
           {
              Schema::create('students', function (Blueprint $table) {
            $table->id();
            $table->string('first_name');
           $table->string('last_name');
            $table->string('middle_name')->nullable();
           $table->string('card_number')->nullable();
          $table->string('card_data')->nullable();
           $table->json('user_information')->nullable();
          $table->json('balances');
          $table->foreignId('user_id')->constrained();
          $table->foreignId('school_id')->constrained('users','school_id');
          $table->timestamps();
      });
  }

           public function down()
        {
       Schema::dropIfExists('students');
      }
       };

User model :

protected $guarded = ['id'];

protected $hidden = [
	'password',
	'remember_token',
];

public function school(): BelongsTo
{
	return $this->belongsTo(School::class);
}

public function students(): HasMany
{
    return $this->hasMany(Student::class);
}

Student model :

class Student extends Model

{ use HasFactory;

 protected $guarded = ['id'];

public function user(): BelongsTo
{
    return $this->belongsTo(User::class);
}

public function school(): BelongsTo
{
    return $this->belongsTo(School::class);
}

public function transactions(): HasMany
{
    return $this->hasMany(Transaction::class);
}

}