Laravel Lighthouse: Passing 2 values on BelongsToMany Pivot

What I'm trying to do is passing 2 extra values on my belongsToMany relation that should be placed on the pivot.

I've read the documentation and found this: https://lighthouse-php.com/6/eloquent/nested-mutations.html#belongstomany

I've tried to replicate it and it works with 1 value. But I'd like to pass 2 values and when I try that it says that for the second value there is no default value. I can't seem te figure out what is going wrong in my mutation...

type AdvancedTreatment {
    id: ID!
    createdAt: DateTime! @rename(attribute: "created_at")
    updatedAt: DateTime! @rename(attribute: "updated_at")
    deletedAt: DateTime @rename(attribute: "deleted_at")
    visit: Visit! @belongsTo
    advancedParameters: [AdvancedParameter] @hasMany
    advancedMedications: [AdvancedMedication!] @belongsToMany
    advancedSampleEvaluation: AdvancedSampleEvaluation @hasOne
    advancedAppliedActions: [AdvancedAppliedAction] @hasMany
    pivot: AdvancedMedicationAdvancedTreatmentPivot!
}

type AdvancedMedicationAdvancedTreatmentPivot{
    advancedAdministrationType: AdvancedAdministrationType!
    administeredDose: String! @rename(attribute: "administered_dose")
}

extend type Mutation {
    saveAdvancedMedications(input: SaveAdvancedMedicationsInput! @spread): AdvancedTreatment! @update
}

input SaveAdvancedMedicationsInput {
    id: ID!
    advancedMedications: UpdateAdvancedMedicationsBelongsToMany
}

input UpdateAdvancedMedicationsBelongsToMany {
    sync: [SyncAdvancedMedicationAdvancedTreatment!]
}

input SyncAdvancedMedicationAdvancedTreatment {
    id: ID!
    advancedAdministrationType: AdvancedAdministrationType! @rename(attribute: "advanced_administration_type")
    administeredDose: String @rename(attribute: "administered_dose")
}

enum AdvancedAdministrationType{
    IV @enum(value: "iv")
    IM @enum(value: "im")
    PO @enum(value: "po")
    SC @enum(value: "sc")
    AERO @enum(value: "aero")
    RECTAL @enum(value: "rect")
    TRANSD @enum(value: "transd")
    NASAL @enum(value: "nasal")
}

My mutation in graphiql:

mutation{
  saveAdvancedMedications(input:{
    id: 1
    advancedMedications:{
      sync: [
        {
          id:1
          advancedAdministrationType: IV
          administeredDose: "1 Dick/gr"
        }
         {
          id:2
            advancedAdministrationType: IM
          administeredDose: "2 Dick/gr"
        }
      ]
    }
  }){
    id
    advancedMedications{
      id
      pivot{
       advancedAdministrationType
        administeredDose
      }
    }
  }
}

It just looks like it won't take my advancedAdministrationType into the query for some reason? is there something that I'm missing or doing

Visualisation om my tables:

My Error message:

EDIT: What I already foudn is that it looks like when using a Pivot model Lighthouse won't let it work

public function advancedMedications(): BelongsToMany
{
    return $this->belongsToMany(AdvancedMedication::class)
        ->using(AdvancedMedicationAdvancedTreatment::class)
        ->withPivot(['administered_dose', 'advanced_administration_type'])
        ->withTimestamps();
}

So When I remove on both sides of the relation

->using(AdvancedMedicationAdvancedTreatment::class)

it will magically work. Is it because I'm missing some properties on the pivot model or because of Lighthouse won't work with pivot models? Hereby my pivot model:

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Relations\BelongsTo;
use Illuminate\Database\Eloquent\Relations\Pivot;

class AdvancedMedicationAdvancedTreatment extends Pivot
{
    protected $fillable = [
        'administered_dose',
        'advanced_administrations_type',
    ];


    /**
     * Belongs to AdvancedMedication.
     */
    public function advancedMedication(): BelongsTo
    {
        return $this->belongsTo(AdvancedMedication::class);
    }

    /**
     * Belongs to AdvancedTreatment.
     */
    public function advancedTreatment(): BelongsTo
    {
        return $this->belongsTo(AdvancedTreatment::class);
    }

}

SOLUTION Remove the fillables solved it all for some reason:

protected $fillable = [
    'administered_dose',
    'advanced_administrations_type',
];

After hours of debugging I found that on a Pivot model you have to remove the fillables to make this work:

In this case I had to remove SOLUTION Remove the fillables solved it all for some reason:

protected $fillable = [
    'administered_dose',
    'advanced_administrations_type',
];