title: Use URL parameter in Contact Form 7 Field
body: <p>I would like to add some PHP in my form created with Contact Form 7, a WordPress plugin.
  I've already tried this but it didn't work: <a href="https://stackoverflow.com/questions/27817294/executing-php-code-in-contact-form-7-textarea">Executing PHP Code in Contact Form 7 Textarea</a>.
  Every time I insert the function, my website crashes.</p>
  
  <p>I have a variable stored in a $_SESSION. I have put that variable in a hidden input and now I would like to take the value of the hidden input and place it in the contact form.
  How can I do this? Thanks!</p>
  
  <p><a href="https://i.stack.imgur.com/0kFia.png" rel="nofollow noreferrer">Screenshot of the website and the hidden input</a></p>
  
  <p><a href="https://i.stack.imgur.com/3hOx8.png" rel="nofollow noreferrer">Screenshot of the back-end of the form</a></p>