App\Http\Requests\CreateInvoiceAPIRequest::rules PHP Method

    public function rules()
    {
        $rules = ['email' => 'required_without:client_id', 'client_id' => 'required_without:email', 'invoice_items' => 'valid_invoice_items', 'invoice_number' => 'unique:invoices,invoice_number,,id,account_id,' . $this->user()->account_id, 'discount' => 'positive'];
        return $rules;
    }