Hi,
In the file administrator/components/com_hikashop/classes/address.php search for the code:
str_replace('{'.$fieldname.'}',
you'll find it on 3 places. In each place, add
just after it to get:
str_replace('{'.$fieldname.'}',(string)
and it will remove these deprecated messages.
We'll add the changes on our end too for the next version.
PS: note that these are not errors. They are messages for developers to update their code for future versions of PHP.
Normally, these deprecated messages shouldn't appear on a live website. So that means that you probably want to check with your hosting why these are being displayed and how to not have deprecated messages.