UUID column is getting NULL on create

Hello guys, I'm having this bizarre problem in my Laravel application. I was migrating all my models to use UUIDs instead of incrementing IDs. I was able to do so for one model without issues. But when I wanted to do the same for the second model, all my tests are blowing up complaining about a NULL value for the ID.

create_clients_table.php

Schema::create('clients', function (Blueprint $table) {
    $table->uuid('id')->primary();
    $table->timestamps();

    // more fields
});

Client.php

use Illuminate\Foundation\Auth\User;

class Client extends User
{
    use HasFactory, HasApiTokens, Notifiable;
    
    protected $fillable = [
        // fillable fields
    ];

    public $incrementing = false;

    protected $keyType = 'string';

    protected $casts = [
        'id' => 'string'
    ];

    protected static function boot()
    {
        parent::boot();

        static::creating(function (Model $model) {
            $model->setAttribute($model->getKeyName(), Uuid::uuid4());
        });
    }

    //
}

ClientController.php

public function store()
{
    $client = Client::where('phone_number', request()->phone_number)->first();

    if (!$client) {
        $client = Client::create([
            // fillable fields
        ]);

        return response()->json($client, 201);
    } else {
        // attempt login
    }
}

The weird thing about this issue is the fact that everything seems to be working fine when I try to create a Client in php artisan tinker. But the tests that back the client creation process and stuff are all failing. What am I missing here? Anything I should check? I'm really lost here.