Fix WordPress Critical Error

My WordPress site is currently down—the front-end shows the dreaded “There has been a critical error” message, so nothing loads. The priority is to get the website back online by resolving whatever is blocking it (very likely a plugin issue, but I need confirmation)... (Budget: $30 - $250 AUD, Jobs: cPanel, HTML, MySQL, PHP, Web Development, Web Hosting, Website Management, WordPress)