Code Injection Footer but just one page

Site URL: https://www.haikuink.com/thank-you-booking-brows

Hi!

I need to add a bit of code to my Purchase Completed page.

The instructions are : "Paste this code just before the closing </body> tag on your purchase completed page."

But when I try code injection for just that page it only allows Header Injection.

I don't want to add this code to every page just this one particular "Thank You" page before the Footer.

That instruction may be an effort to get the code to run later in the page load cycle.

Without being able to see the code it's hard to give advice. But one thing you can try is to wrap the code in the following.

window.addEventListener ( 'DOMContentLoaded', ( ) => {

  /* javascript code here */
  
  } );

This code delays code inserted where indicated until later in the page load cycle.