You don’t need to change it. The email shows “Paid deposit” if the deposit was paid. And “Required deposit” if it was not paid. Those are two different scenarios and you don’t need to modify the strings. They are already correct.
Can you remove your modification and do another similar reservation? Then share the URL of the confirmation page and a screenshot of the email.
To pay a deposit, you need to use PayPal or Stripe and have the booking mode set to “Instant booking”. What is you booking mode? was the reservation paid with PayPal or Stripe?