Laravel 5.7 - Invalid text representation: 7 ERROR: invalid input syntax for integer: \"10337e35-8da9-4600-b7de-792398eb6f48\"

I'm trying to create a database notifcation in Laravel 5.7 and getting this SQL QueryException. My $notifiable variable in the toArray method is the user and this id in the exception: invalid input syntax for integer: \"10337e35-8da9-4600-b7de-792398eb6f48\" is the correct id for the user to be notified. I have my notifications table set up in the standard way:

Schema::create('notifications', function (Blueprint $table) {
        $table->uuid('id')->primary();
        $table->string('type');
        $table->morphs('notifiable');
        $table->text('data');
        $table->timestamp('read_at')->nullable();
        $table->timestamps();
    });

My user table is set up like this:

Schema::create('users', function (Blueprint $table) {
        $table->uuid('id');
        $table->primary('id');
        $table->string('name');
        $table->string('username')->unique();
        $table->string('email');
        $table->string('password');
        $table->rememberToken();
        $table->timestamps();
        $table->softDeletes();
    });

It is set up with a uuid as the primary id. Beyond that, the notification itself has database in the via method:

public function via($notifiable)
{
    return ['database', 'mail'];
}

I've set a couple properties in the toArray method. Nothing complicated. I'm not seeing the logical cause for this exception.

via Chebli Mohamed