Since PLESK 10, I’ve observed that one of the most common mistakes made on Plesk is the subscription expiration. This is usually neglected when PLESK is created under service provider view. Any subscription created with default settings has a 12 month validity period and will be automatically suspended by PLESK when it is expired. If you are seeing website returns a 503 page or service unavailable and this is likely the cause.
To verify your settings, sign in as admin, root or administrator to your Plesk Panel. From the menu on the left-hand side, select Subscription. Now, select the subscription highlighted in “RED” with an exclamation mark and choose “Customize”.
Scroll all the way down, you will find the expiration date section. To rectify, check on unlimited or select a later date and “Update”.
Remember to hit on the “Activate button” if your subscription has been suspended.