Unable to open WordPress instance in Plesk: eval()’d code on line 1

Symptoms

• The following error is shown when opening a WordPress instance at WordPress > example.com page:

  PHP Parse error: syntax error, unexpected '?' in /usr/share/plesk-wp-cli/php/WP_CLI/Runner.php(996): eval()'d code on line 1

• Symbols like <U+FEEF> can be observed in the beginning of the wp-config.php file over command-line interface using less tool:

  # less /var/www/vhosts/example.com/httpdocs/wp-config.php
  <U+FEFF><?php
  ...

Cause

Hidden incorrect symbols in wp-config.php file.

Resolution

1. Log in to the server via SSH.

2. Rename the current wp-config.php file.

   # mv /var/www/vhosts/example.com/httpdocs/wp-config.php{,.orig}

3. Create a new one by copying the content from the renamed file using cat tool:

   # cat /var/www/vhosts/example.com/httpdocs/wp-config.php.orig > /var/www/vhosts/example.com/httpdocs/wp-config.php

Note: replace example.com with the actual domain's name in the commands above.