Solving Drupal 8 Invalid Host Name Problem in PHP

If an existing Drupal 8 encounters the error "The provided host name is not valid for this server" when using a different domain name or IP address, then the following steps may help resolve the issue.

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1. In the Drupal folder, open the file that handles the Drupal settings.

sites/default/settings.php

2. Find the "Trusted host configuration" section and add the lines marked "TRUSTED" as follows.

// BEGIN CODE

/**
 * Trusted host configuration.
 ...
 */

$settings['trusted_host_patterns'] = [
        '^localhost$', // TRUSTED loopback host name
        '^localhost\:', // TRUSTED loopback port nums
        '^127\.', // TRUSTED loopback IPv4 addresses
        '^\[\:\:1\]', // TRUSTED loopback IPv6 address
        '\.local$', // TRUSTED mDNS top-level domain name for LAN
        '\.local\:', // TRUSTED mDNS top-level domain port for LAN
        '^192\.168\.', // TRUSTED single Class B network IPv4
        '^10\.', // TRUSTED single Class A network IPv4
        '^mydomain\.com$', // TRUSTED Internet domain name
        '\.mydomain\.com$', // TRUSTED Internet subdomain names
];

// END CODE

3. Save the file and reload the page.

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