What is the difference between Service Locator and class with 2+ methods?

service_locator.php

<?php

/*
 *
 * What is the difference between Service Locator and class with 2+ methods?
 *
 */

// We have class with two methods
class InvoiceService implements InvoiceServiceInterface
{
    private $invoiceSender;
    private $invoiceGenerator;

    public function __construct(InvoiceSenderInterface $invoiceSender, InvoiceGeneratorInterface $invoiceGenerator)
    {
        $this->invoiceSender = $invoiceSender;
        $this->invoiceGenerator = $invoiceGenerator;
    }

    // This method is unit of logic that we need to run
    public function sendInvoice(Payment $payment)
    {
        $this->invoiceSender->send($payment->getInvoice());
    }

    public function createInvoiceForPayment(Payment $payment)
    {
        $invoice = $this->invoiceGenerator->generate($payment);

        $payment->setInvoice($invoice);
        $payment->save();
    }
}

// We use service locator to get (as we think) some service (unit of logic) to run logic (send invoice)
class PaymentService
{
    private $serviceLocator;

    public function __construct(ServiceLocator $serviceLocator)
    {
        $this->serviceLocator = $serviceLocator;
    }

    public function capturePayment(Payment $payment)
    {
        $payment->setCaptured();
        $payment->save();

        $this->serviceLocator->get(InvoiceServiceInterface::class)->sendInvoice($payment);
    }
}

// We use class with 2 methods to do the same
class OtherPaymentService
{
    private $invoiceService;

    public function __construct(InvoiceService $invoiceService)
    {
        $this->invoiceService = $invoiceService;
    }

    public function capturePayment(Payment $payment)
    {
        $payment->setCaptured();
        $payment->save();

        $this->invoiceService->sendInvoice($payment);
    }
}

// But in fact we use that class as service locator for real service (unit of logic) - THE METHOD
class OtherPaymentServiceForShowingProblem
{
    private $invoiceService;

    public function __construct(InvoiceService $invoiceService)
    {
        $this->invoiceService = $invoiceService;
    }

    public function capturePayment(Payment $payment)
    {
        $payment->setCaptured();
        $payment->save();

        // get unit of logic that we want to run by method name and run it
        $unitOfLogic = $this->invoiceService->getMethod('sendInvoice');
        $unitOfLogic($payment);

        // ^^^ Here above we are using class with 2 methods as service locator (unit of logic locator)
        // And by doing it we inject hidden unused dependency - second method of that class
    }
}