invoiceninja/app/Models/PaymentLibrary.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

/**
 * Class PaymentLibrary.
 */
class PaymentLibrary extends Model
{

    /**
     * @return \Illuminate\Database\Eloquent\Relations\HasMany
     */
    public function gateways()
    {
        return $this->hasMany(Gateway::class, 'payment_library_id');
    }
}