Pivot table-what's wrong with this setup?

[Ifriqiya]

I have a pivot table for two models and the eloquent relationships are also defined. I'm getting this error when I run my static analysis: Access to an undefined property App\Models\InvestmentServiceProvider::$pivot from the third line of code below:

$investmentServiceProviders = $financialGoal->investmentServiceProviders;
foreach ($investmentServiceProviders as $investmentServiceProvider) {
$amount = $investmentServiceProvider->pivot->amount;  //trying get this value from the pivot table
//
}

These are my model relationship methods in the FinancialGoal and InvestmentServiceProvider models respectively:

    /**
     * @return \Illuminate\Database\Eloquent\Relations\BelongsToMany<\App\Models\InvestmentServiceProvider>
     */
    public function investmentServiceProviders()
    {
        return $this->belongsToMany(InvestmentServiceProvider::class,
            'financial_goal_investment_service_provider', 'goal_id', 'investment_service_provider_id')
        ->withPivot('is_authorised', 'amount');
    }

    /**
     * @return \Illuminate\Database\Eloquent\Relations\BelongsToMany<\App\Models\FinancialGoal>
     */
    public function financialGoals()
    {
        return $this->belongsToMany(FinancialGoal::class,
            'financial_goal_investment_service_provider', 'investment_service_provider_id', 'goal_id')
        ->withPivot('is_authorised', 'amount');
    }

This is my pivot table migration code:

<?php

use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;

return new class extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('financial_goal_investment_service_provider', function (Blueprint $table) {
            $table->id();
            $table->char('goal_id', 36);
            $table->foreign('goal_id')->references('id')->on('financial_goals')->cascadeOnDelete();
            $table->foreignId('investment_service_provider_id')->constrained()
            ->index('fg_investment_service_provider_id')->cascadeOnDelete();
            $table->boolean('is_authorised')->default(false);
            $table->decimal('amount', 15, 2)->nullable();
            $table->timestamps();
        });
    }

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

I believe this follows the Laravel docs and should work and I'm at a loss as to why it's not.