[2020] Nested serializers: Server Error 500

class RacuniizlaznifinancijskiSerializers(serializers.ModelSerializer):
    pp = PoslovnipartneriSerializers(many=True, read_only=True)
class Meta:
        model = Racuniizlaznifinancijski
        fields = ["__all__", "pp"]

I want all fields from Racuniizlaznifinancijski and also all fields from Poslovnipartneri...

What is wrong here?