Error during the reconfiguration of the Apache files in Plesk: Invalid command ‘RequestHeader’, perhaps misspelled or defined by a module not included in the server configuration

Symptoms

• Execution of the plesk repair web command returns the next error message:

  AH00526: Syntax error on line 117 of /etc/apache2/plesk.conf.d/server.conf:
  Invalid command 'RequestHeader', perhaps misspelled or defined by a module not included in the server configuration

Cause

All Apache modules are disabled.

Resolution

1. Log into Plesk
2. Go to Tools & Settings > Apache Web Server
3. Enable modules as on the screenshot below and press the OK button to apply the changes:
   
4. Log into the server via SSH
5. Execute the command below to repair the Apache configuration:

   # plesk repair web