I have a form on a page. On this form I have a DropdownField. This Dropdown should be filled with Data, which is filtered.

This is my code

     public function SpieleForm() {
         //Debug::dump($dataToEdit); die;
         if ($this->request->param("OtherID")){
         $dataToEdit = Spiele::get()->byID($this->request->param("OtherID"));
		}

        // Felder für Formular vorbereiten
		$fields = new FieldList(
		    DateField::create("Datum", "Datum (Klicken für Kalender)")
			->setConfig( "showcalendar", true ),
			TimeField::create("Uhrzeit", "Uhrzeit"),
			DropdownField::create('StadionID', 'Stadion', Stadion::get()->map('ID', 'Name')),
			DropdownField::create("GruppeID","Gruppe", Gruppen::get()->map('ID', 'Name'))->setEmptyString('(Bitte auswählen)'),
		    DropdownField::create("HeimID","Heimteam", Teams::get()->filter(array("Saison.ID" => $this->request->param("ID")))->map('ID', 'Name')->toArray())->setEmptyString('(Bitte auswählen)'),
		    TextField::create("H1","Pkt Heim 1.Viertel"),
		    TextField::create("H2","Pkt Heim 2.Viertel"),
		    TextField::create("H3","Pkt Heim 3.Viertel"),
		    TextField::create("H4","Pkt Heim 4.Viertel"),
		    TextField::create("PktHeim","Pkt Heim Gesamt"),
		    DropdownField::create("GastID","Gastteam", Teams::get()->map('ID', 'Name')->toArray())->setEmptyString('(Bitte auswählen)'),
		    TextField::create("G1","Pkt Gast 1.Viertel"),
		    TextField::create("G2","Pkt Gast 2.Viertel"),
		    TextField::create("G3","Pkt Gast 3.Viertel"),
		    TextField::create("G4","Pkt Gast 4.Viertel"),
		    TextField::create("PktGast","Pkt Gast Gesamt"),
		    DropdownField::create("StatusID","Status", Status::get()->map()->toArray()),
		    HiddenField::create("ID","ID"),
		    HiddenField::create("SaisonID","SaisonID",$this->request->param("ID"))
            
           
        );

        $actions = new FieldList(
            FormAction::create("SpieleEintragen","Eintragen")
        );

        $form = new Form($this, 'SpieleForm', $fields, $actions);
		$form->loadDataFrom($dataToEdit);
           
		return $form;
		}
	

The Data Model Teams has $many_many with the Data Model "Saison".
I get the right teams in my dropdown, but I can't save it. A validation error occurs and says the value of the ID is not valid.
I can save the data when i change variable $this->request->param("ID") to a number. For example 1. The it works and that seems really strange.