Modifying translations - not working when trying to edit the body

[ParcoMolo]

Hi Ladies and Gents,

I wanted to edit the "Shipped" email's body so that I can add the tracking number ({followup} / {shipping_number}, but when trying to modify the translation as shown (Screenshot 1) below, then it fails (Screenshot 2).

(Screenshot 1)

 

(Screenshot 2)

/opt/bitnami/apps/prestashop/htdocs/mails/en/credit_slip.html cannot be copied to /opt/bitnami/apps/prestashop/htdocs/themes/classic/mails/en/credit_slip.html

I could edit the "Package in transit" email (when modifying the Email Subject), but would really rather prefer to be able to edit the "Shipping" email.

 

Thanks in advance for any advice/help.

 

Edited March 25, 2021 by ParcoMolo
Added the text that you get when trying to edit the email subject and removed unnecessary screenshot (see edit history)