'Drupal 8 - outage screen shows " The Specific URL cannot found" error

Recently WAF has been implemenent in my project to enhance network security. Whenever I go to maintenance mode window ,enter the outage and click save configurations " The Specific URL cannot found" error shows up.

I am facing this error from a long time. After check online forums I found that WAF blocks 503 status code and does let drupal site to operate in Outage.

I am trying to use this modulue to throws 503 https://www.drupal.org/project/maintenance200

Is anyone aware of this issue.??



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