Using the Legacy html buttons, does the buy now button now have to have the same delivery url as the url in the now changed PaypalIPN? Do we have to change 'ipnpb.' to 'www.'?

Here's part of my PaypalIPN.php - notice I've changed the sandbox url to www but kept the paypal/cgi-bin @ ipnpb

/** @Var bool Indicates if the sandbox endpoint is used. */
private $use_sandbox = false;
/** @Var bool Indicates if the local certificates are used. */
private $use_local_certs = false;

/** Production Postback URL */
const VERIFY_URI = 'https://ipnpb.paypal.com/cgi-bin/webscr';
/** Sandbox Postback URL */
const SANDBOX_VERIFY_URI = 'https://www.sandbox.paypal.com/cgi-bin/webscr';
/** 22/10/22 STEVE changed above url from ipnpb. to www. as on PayPal Community

/** Response from PayPal indicating validation was successful */
const VALID = 'VERIFIED';
/** Response from PayPal indicating validation failed */
const INVALID = 'INVALID';

/**
* Sets the IPN verification to sandbox mode (for use when testing,
* should not be enabled in production).
* @RETURN void
*/
public function useSandbox()
{
$this->use_sandbox = true;
}

My next question is, the html button generator put the www. in automatically - there's no ipnpb - see part of my Buy Now script:
<form target="paypal" action="https://www.paypal.com/cgi-bin/webscr" method="post" >
I'd be truly grateful for any advice given, my payments have been so eratic for the past 2 years!!