validation.in on form submit

Select::make('matieres')
      ->label('Matière(s)')
      ->multiple()
      ->relationship('matieres', 'nom')
      ->options(Matiere::whereHas('sessions', function ($Query) {
          $Query->where('session_id', '=', Filament::getTenant()->id);
      })->get()->sortBy(function ($matiere) {
          return $matiere->nom;  // Sort by the accessor value
      })
          ->mapWithKeys(function ($matiere) {
              return [$matiere->id => $matiere->nom];  // Uses the getNomAttribute() accessor
          }))
      ->preload()
      ->live()
      -required()

public function matieres(): BelongsToMany
    {
        return $this->belongsToMany(Matiere::class);
    }